Move shared clock.c file and per-SoC clock-xxx.c files
to only build when CONFIG_COMMON_CLK != y.

The regular ARCH_SHMOBILE case with legacy SH clock framework
will build just as before with this patch applied, however
the case when COMMON_CLK=y will exclude all the clock files.
Signed-off-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>