ARM: shmobile: Introduce a Kconfig entry for R-Car Gen2

Add a Kconfig entry for R-Car Generation 2 SoCs that
enables CMT timer and the IRQC interrupt driver.

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>