Preparation to enable -Wimplicit-fallthrough in build flags

[anglov]

Description

Motivation and Context

Preparation to enable -Wimplicit-fallthrough in build flags

Types of changes

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Chore (refactoring, style fixes, git/CI config, submodule management, no code logic changes)

How Has This Been Tested?

• Already covered by automatic testing.
• New test added: (add PR link here).
• Tested by hand on: (list targets here).

Checklist:

• My change requires a change to the documentation.
• I have updated the documentation accordingly.
• I have added tests to cover my changes.
• All new and existing linter checks and tests passed.
• My changes generate no new compilation warnings for any of the targets.

Special treatment

• This PR needs additional PRs to work (list the PRs, preferably in merge-order).
• I will merge this PR by myself when appropriate.

[gemini-code-assist]

Code Review

This pull request adds explicit /* fallthrough */ comments to switch-case statements in hal/riscv64/dtb.c and lib/format.c to clarify intentional fall-through behavior, and adds a state reset in devices/tty-bios/tty-bios.c. The reviewer suggests using a fall-through comment in devices/tty-bios/tty-bios.c as well to avoid duplicating the reset logic before the default case.

[github-actions]

Unit Test Results

10 890 tests  +305   10 220 ✅ +306   53m 15s ⏱️ -2s
   680 suites + 31      670 💤 ±  0 
     1 files   ±  0        0 ❌  -   1 

Results for commit 2618978. ± Comparison against base commit a139fa2.

This pull request removes 3 and adds 308 tests. Note that renamed tests count towards both.

phoenix-rtos-tests/libcache/unit ‑ armv7m4-stm32l4x6-nucleo:phoenix-rtos-tests/libcache/unit
phoenix-rtos-tests/libcache/unit ‑ armv7m7-imxrt106x-evk:phoenix-rtos-tests/libcache/unit
phoenix-rtos-tests/libcache/unit ‑ armv7m7-imxrt117x-evk:phoenix-rtos-tests/libcache/unit

phoenix-rtos-tests/libc/posixsrv ‑ aarch64a53-zynqmp-qemu:phoenix-rtos-tests/libc/posixsrv.tmpfile.basic
phoenix-rtos-tests/libc/posixsrv ‑ aarch64a53-zynqmp-qemu:phoenix-rtos-tests/libc/posixsrv.tmpfile.binary
phoenix-rtos-tests/libc/posixsrv ‑ aarch64a53-zynqmp-qemu:phoenix-rtos-tests/libc/posixsrv.tmpfile.multiple
phoenix-rtos-tests/libc/posixsrv ‑ armv7a7-imx6ull-evk:phoenix-rtos-tests/libc/posixsrv.tmpfile.basic
phoenix-rtos-tests/libc/posixsrv ‑ armv7a7-imx6ull-evk:phoenix-rtos-tests/libc/posixsrv.tmpfile.binary
phoenix-rtos-tests/libc/posixsrv ‑ armv7a7-imx6ull-evk:phoenix-rtos-tests/libc/posixsrv.tmpfile.multiple
phoenix-rtos-tests/libc/posixsrv ‑ armv7a9-zynq7000-qemu:phoenix-rtos-tests/libc/posixsrv.tmpfile.basic
phoenix-rtos-tests/libc/posixsrv ‑ armv7a9-zynq7000-qemu:phoenix-rtos-tests/libc/posixsrv.tmpfile.binary
phoenix-rtos-tests/libc/posixsrv ‑ armv7a9-zynq7000-qemu:phoenix-rtos-tests/libc/posixsrv.tmpfile.multiple
phoenix-rtos-tests/libc/posixsrv ‑ armv7a9-zynq7000-zedboard:phoenix-rtos-tests/libc/posixsrv.tmpfile.basic
…

♻️ This comment has been updated with latest results.

[anglov]

@lukileczo could you look into riscv dtb parsing? I think that fallthrough is valid but would be great to confirm

[lukileczo]

@lukileczo could you look into riscv dtb parsing? I think that fallthrough is valid but would be great to confirm

Yes, the fallthrough is intentional there