octeontx2-af: CN20k basic mbox operations and structures

octeontx2-af: CN20k basic mbox operations and structures

This patch adds basic mbox operation APIs and structures to add support
for mbox module on CN20k silicon. There are few CSR offsets, interrupts
changed between CN20k and prior Octeon series of devices.

Signed-off-by: Sai Krishna <saikrishnag@marvell.com>
Signed-off-by: Sunil Kovvuri Goutham <sgoutham@marvell.com>
Signed-off-by: Subbaraya Sundeep <sbhatta@marvell.com>
Link: https://patch.msgid.link/1749639716-13868-3-git-send-email-sbhatta@marvell.com
Signed-off-by: Jakub Kicinski <kuba@kernel.org>