ARM: shmobile: Add pinctrl_register_mappings() for Koelsch

Add code to setup the r8a7791 PFC for the Koelsch board.

At this point serial consoles are added, and in the near
future other platform-device-only devices will be added
here like for instance the r8a7791 DU.

Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>