ARM: shmobile: sh73a0: Update DTS to include CPU frequency

Add CPU Frequency information to the sh73a0 DTS file. This
will allow us to use the shared C code on sh73a0 and KZM9G
which reads out the clock frequency from DT and calculates the
delay settings from there.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>