Documentation: coresight: Panic support

Add documentation on using coresight during panic
and watchdog.

Signed-off-by: Linu Cherian <lcherian@marvell.com>
Signed-off-by: Suzuki K Poulose <suzuki.poulose@arm.com>
Link: https://lore.kernel.org/r/20250212114918.548431-9-lcherian@marvell.com