mlxsw: reg: Add XRALXX Registers

Add a couple of registers used to manipulate LPM trees on XM:
The XRALTA is used to allocate the XLT LPM trees.
The XRALST is used to set and query the structure of an XLT LPM tree.
The XRALTB register is used to bind virtual router and protocol to
an allocated LPM tree.

Since the XM registers are identical to the legacy router registers
with a fixed offset, re-use their pack functions.

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