ARM: shmobile: Introduce a Kconfig entry for R-Mobile

Add a Kconfig entry for R-Mobile SoCs that enables
both CMT and TMU timers. Interrupt controller varies
with SoC version so it is excluded.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>