samples: tests: mbox: Add lpcpresso55s69 support

This commit adds support for NXP board LPCXpresso55S69 for mbox.
 - samples/drivers/mbox/ - mbox signaling mode
 - samples/drivers/mbox_data/ - mbox data transfer mode
 - tests/drivers/mbox/mbox_data/ - mbox test to verify functionality.

Signed-off-by: Tomas Galbicka <tomas.galbicka@nxp.com>