RTT: `LOG_PANIC` unable to be called in ISR's

[JordanYates]

Describe the bug

Calling LOG_PANIC() in an exception handler when RTT is the logging backend will deadlock due to triggering its own assertion. This is due to SEGGER_RTT_LOCK not being suitable for use in IRQ's:

zephyr/modules/segger/SEGGER_RTT_zephyr.c

Lines 35 to 38 in 7773fe8

	void zephyr_rtt_mutex_lock(void)
	{
	k_mutex_lock(&rtt_term_mutex, K_FOREVER);
	}

While mutex locking is explicitly not permitted in ISRs:

zephyr/include/zephyr/kernel.h

Line 3066 in 7773fe8

* Mutexes may not be locked in ISRs.

Expected behavior

LOG_PANIC should never deadlock.

Impact

System lockup on exception unless a hardware watchdog that automatically reboots is enabled.

Logs and console output