arch/atomic: remove up_testset in spinlock

[zhangyu-duck]

Summary

Remove the per-arch testset implementation from the spinlock layer. The testset abstraction predates the unified spinlock.h API and is no longer used now that all arches provide spin_lock_irqsave()/spin_unlock_irqrestore() directly.

Changes

• Delete arch/<arch>/include/spinlock.h and the per-arch *_testset.{c,S} implementations for arm, sim, sparc, tricore, x86_64, xtensa
• Drop the CXD56_TESTSET, CXD56_TESTSET_WITH_HWSEM, and CXD56_ATOMIC_WITH_HWSEM Kconfig options from arch/arm/src/cxd56xx/Kconfig
• Simplify the CXD56 semaphore pool loop in cxd56_sph.c to a single for (i = 3; i < 15; i++) path
• Clean up the SMP/testset references in Documentation/

Impact

• Archs that previously relied on testset for spinlock must now provide spin_lock_irqsave()/spin_unlock_irqrestore() via arch/<arch>/include/spinlock.h (or the default up_irq_save()/up_irq_restore() fallback in include/nuttx/spinlock.h). All currently-supported arches already do this.
• CXD56 no longer exposes the custom testset/hwsem config knobs; its spinlock path falls back to the generic IRQ-based implementation.
• No functional change for arches that were already using the unified spinlock API.

[github-actions]

MemBrowse Memory Report

qemu-armv8a

• Code: .text +64 B, .text._assert -40 B, .text.clock_initialize -44 B, .text.exec_getsymtab -36 B, .text.fdlist_close -36 B, .text.fdlist_dupfile -88 B, .text.fdlist_extend -56 B, .text.fdlist_get_by_index -44 B, .text.fdlist_install.isra.0 -44 B, .text.file_mq_timedsend_internal -92 B, .text.gethostname -44 B, .text.group_alloc_child -48 B, .text.group_exit_child -36 B, .text.group_find_child -36 B, .text.group_free_child -36 B, .text.group_join -36 B, .text.group_leave -36 B, .text.group_remove_child -36 B, .text.group_remove_children -44 B, .text.irq_attach -44 B, .text.mcount_internal -36 B, .text.moncontrol -72 B, .text.monstartup -40 B, .text.nxclock_gettime -36 B, .text.nxmq_free_msg -68 B, .text.nxsig_action -232 B, .text.nxsig_find_action -40 B, .text.nxsig_pendingset -44 B, .text.nxsig_release -140 B, .text.nxsig_release_action -36 B, .text.nxsig_remove_pendingsignal -20 B, .text.nxsig_tcbdispatch -80 B, .text.pl011_txint -40 B, .text.profil -36 B, .text.profil_timer_handler -36 B, .text.spinlock_t_test_thread -36 B, .text.timer_create -92 B, .text.timer_deleteall -36 B, .text.timer_gethandle -36 B, .text.timer_release -48 B, .text.up_putc -44 B, .text.work_qcancel -36 B, .text.work_queue_wq -36 B, .text.work_thread -84 B (-0.7%, 335,292 B)
• Data: .bss.g_assert_lock -4 B, .bss.g_basetime_lock -4 B, .bss.g_child_pool_lock -4 B, .bss.g_exec_lock -4 B, .bss.g_hostname_lock -4 B, .bss.g_irqlock -4 B, .bss.g_kthread_group -8 B, .bss.g_locktimers -4 B, .bss.g_msgfreelock -4 B, .bss.g_sigaction_spin -4 B, .data.g_hpwork -8 B, .data.g_uart1priv -8 B (-0.1%, 77,466 B)
  No memory changes detected for:
• arduino-mega2560
• esp32-devkitc
• hifive1-revb
• mirtoo
• qemu-intel64
• rx65n-rsk2mb
• s698pm-dkit
• stm32-nucleo-f103rb