mlxsw: spectrum: Propagate context from work handler containing RALUE payload

Currently, RALUE payload is defined locally in the function that is
calling the register write. With introduction of alternative register to
RALUE, XMDR, it has to be possible to put multiple FIB entry
operations into single register write.

So in order to prepare for that, have per-work entry operation context
and propagate it all the way down to the functions writing RALUE.

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