ARM: shmobile: r8a7778: Use shmobile_init_delay()

Adjust the r8a7778 SoC support code to use shmobile_init_delay()
together with CPU Frequency settings from the DTS. Get rid of the
C code version.

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