ARM: shmobile: r8a7792: basic SoC support

Add minimal support for the R-Car V2H (R8A7792) SoC.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>