kirkwood: add save functionality kirkwood_mpp_conf function
If a second non NULL argument is given to the kirkwood_mpp_conf
function, it will be used to store the current configuration of the MPP
registers. mpp_save must be a preallocated table of the same size as
mpp_list and it must be zero terminated as well.
A later call to kirkwood_mpp_conf function with this saved list as first
(mpp_conf) argment will set the configuration back.
Signed-off-by: Valentin Longchamp <valentin.longchamp@keymile.com>
cc: Holger Brunck <holger.brunck@keymile.com>
cc: Prafulla Wadaskar <prafulla@marvell.com>