octeontx2-af: Add new mbox messages to retrieve MCAM entries

This patch introduces new mailbox mesages to retrieve a given
MCAM entry or base flow steering rule of a VF installed by its
parent PF. This helps while updating the existing MCAM rules
with out re-framing the whole mailbox request again. The INSTALL
FLOW mailbox consumer can read-modify-write the existing entry.
Similarly while installing new flow rules for a VF, the base
flow steering rule match creteria is copied to the new flow rule
and the deltas are appended to the new rule.

Signed-off-by: Naveen Mamindlapalli <naveenm@marvell.com>
Co-developed-by: Vamsi Attunuru <vattunuru@marvell.com>
Signed-off-by: Vamsi Attunuru <vattunuru@marvell.com>
Signed-off-by: Sunil Goutham <sgoutham@marvell.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>