eth: fbnic: Add mailbox support for PLDM updates

Add three new mailbox messages to support PLDM upgrades:

* FW_START_UPGRADE - Enables driver to request starting a firmware upgrade
                     by specifying the component to be upgraded and its
		     size.
* WRITE_CHUNK      - Allows firmware to request driver to send a chunk of
                     data at the specified offset.
* FINISH_UPGRADE   - Allows firmware to cancel the upgrade process and
                     return an error.

Signed-off-by: Lee Trager <lee@trager.us>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Link: https://patch.msgid.link/20250512190109.2475614-5-lee@trager.us


Signed-off-by: Paolo Abeni <pabeni@redhat.com>