ipc3: Fix spinlock violation in PM context save on fuzzer

Fix spinlock validation assertion failure during fuzzing on native_sim
builds with IPC3.

Recent Zephyr commit added spinlock validation that detects context
switching while holding spinlocks. This revealed that
`ipc_pm_context_save` calls `arch_irq_lock` before the EDF work queue
yields, causing:

ASSERTION FAIL [arch_irq_unlocked(key) || ...] Context switching while
holding lock!

The hardware PM operations (arch_irq_lock, platform_timer_stop, etc.)
are not needed for POSIX simulation environments. Extend the existing
guard to exclude these operations when CONFIG_ZEPHYR_POSIX is defined.

This preserves PM functionality while avoiding spinlock violations in
native simulation builds.

Signed-off-by: Tomasz Leman <tomasz.m.leman@intel.com>

Author: tmleman

src/ipc/ipc3/handler.c

@@ -672,7 +672,7 @@ static int ipc_pm_context_save(uint32_t header)
 	/* do platform specific suspending */
 	platform_context_save(sof_get());
 
-#if !defined(CONFIG_LIBRARY)
+#if !defined(CONFIG_LIBRARY) && !defined(CONFIG_ZEPHYR_POSIX)
 	/* TODO: check we are inactive - all streams are suspended */
 
 	/* TODO: mask ALL platform interrupts except DMA */