ARM: shmobile: r8a7778: use fixed ratio clock

R-Car M1 has many clocks, and it is possible to
read/use clock ratio of these clocks from FRQMRx.
But, these ratio are fixed value and
these are decided by MD pin status.

This patch reads MD pin status,
and used fixed ratio clock for other clocks.
It was tesed on bock-w board.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>