pinctrl: mvebu: armada-370: provide generic mpp callbacks

We want to get rid of passing register addresses to common pinctrl
driver, so provide set/get callbacks that use generic mpp pins helper
and will be used later.

Signed-off-by: Sebastian Hesselbarth <sebastian.hesselbarth@gmail.com>

diff --cc drivers/pinctrl/mvebu/pinctrl-armada-370.c
Simple merge