NanoPC-T6: align RK806 reset handling with FriendlyARM semantics

[Copilot]

The reset button behavior on NanoPC-T6 remained inconsistent across kernel variants (nabam-rockchip vs FriendlyARM). This PR tightens the RK806 reset path to match FriendlyARM’s low-level PMIC semantics more explicitly, so reset-mode selection is no longer ambiguous at the driver layer.

• RK806 reset property resolution

  • Updated the NanoPC-T6 kernel compatibility patch (rk8xx-core.c) to follow FriendlyARM-style precedence:
    1. pmic-reset-func
    2. fallback to rockchip,reset-mode
    3. default to mode 0 when neither is present
  • Removes the previous behavior that effectively skipped configuration when properties were absent.

• NanoPC-T6 reset docs

  • Updated reset-path documentation to reflect the exact precedence/default behavior now implemented by the compatibility patch.

if (device_property_read_u32(dev, "pmic-reset-func", &rst_fun) &&
    device_property_read_u32(dev, "rockchip,reset-mode", &rst_fun))
    rst_fun = 0;

---

💡 You can make Copilot smarter by setting up custom instructions, customizing its development environment and configuring Model Context Protocol (MCP) servers. Learn more Copilot coding agent tips in the docs.