ARM: shmobile: rcar-gen2: Cache Mode Monitor Register Value

The MD pins are sampled at reset time, hence the read value will always be
the same, and we can avoid the overhead of ioremapping the register on
every read.

Signed-off-by: Geert Uytterhoeven <geert+renesas@linux-m68k.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>