octeontx2-af: Modify nix_vtag_cfg mailbox to support TX VTAG entries

This patch modifies the existing nix_vtag_config mailbox message
to allocate and free TX VTAG entries as requested by a NIX PF.
The TX VTAG entries are global resource that shared by all PFs
and each entry specifies the size of VTAG to insert and the VTAG
header data to insert. The mailbox response contains the entry
index which is used by mailbox requester in configuring the
NPC_TX_VTAG_ACTION for any MCAM entry.

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