ARM: shmobile: Update r7s72100 DTS to include CPU frequency

Add CPU Frequency information to the r7s72100 DTS file. This
will allow us to use the shared C code on r7s72100 and Genmai
which reads out the clock frequency from DT and calculates the
delay settings from there.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Acked-by: Geert Uytterhoeven <geert@linux-m68k.org>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>