ARM: shmobile: sh7372: Update DTS to include CPU frequency

Add CPU Frequency information to the sh7372 DTS file. This
will allow us to use the shared C code on sh7372 and Mackerel
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>