arm: shmobile: r7s72100: add i2c clocks

Tested with RIIC2 on a genmai board. Others untested but hopefully
trivial enough to be added.

Signed-off-by: Wolfram Sang <wsa@sang-engineering.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>