ARM: shmobile: r8a7779: Add helper to read mode pins

Add and use helper to read mode pins.
This will be re-used when moving marzen-reference to
the common clock framework.

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>

diff --cc arch/arm/mach-shmobile/clock-r8a7779.c
Simple merge

diff --cc arch/arm/mach-shmobile/include/mach/r8a7779.h
Simple merge

diff --cc arch/arm/mach-shmobile/setup-r8a7779.c
Simple merge