common/octeontx2: add AF to PF mailbox IRQ and msg handlers

common/octeontx2: add AF to PF mailbox IRQ and msg handlers

This patch adds support for AF to PF mailbox interrupt and message
handling. PF writes the message on mapped mailbox region
followed by writing the mailbox doorbell register. Upon receiving,
the mailbox request in AF(In Linux kernel), It processes the messages
and update the counter memory and update the AF mbox doorbell
register. That would trigger a VFIO interrupt to userspace and
otx2_process_msgs() will handle it.

Signed-off-by: Nithin Dabilpuram <ndabilpuram@marvell.com>
Signed-off-by: Vamsi Attunuru <vattunuru@marvell.com>