ARM: shmobile: r8a7778: Update DTS to include CPU frequency

Add CPU Frequency information to the r8a7778 DTS file. This
will allow us to use the shared C code on r8a7778 and BockW
which reads out the clock frequency from DT and calculates the
delay settings from there.

Also add other missing CPU information to the r8a7778 DTS.

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