mlxsw: spectrum_router: Use RALUE-independent op arg

Since the write/delete of FIB entry is going to be implemented by XMDR
register for XM implementation, introduce RALUE-independent enum for op
so the enum could be used in both RALUE and XMDR.

Signed-off-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: Ido Schimmel <idosch@nvidia.com>
Signed-off-by: Jakub Kicinski <kuba@kernel.org>