ARM: shmobile: rcar-gen2: Correct arch timer frequency on R-Car V2H

According to the datasheet, the frequency of the ARM architecture timer
on R-Car V2H depends on the frequency of the ZS clock, just like on
R-Car E2.

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