ARM: shmobile: R-Car Gen2: CONFIG_COMMON_CLK is always set

Since commit e0426818 ("ARM: shmobile: r8a7790: Remove legacy
code"), all R-Car Gen2 SoCs are supported by multiplatform kernels only.
As CONFIG_COMMON_CLK is always set for multiplatform kernels, we can
remove related #ifdefs in code specific to R-Car Gen2 SoCs.

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