ARM: shmobile: Use r8a7740 DT CPU Frequency for Armadillo DT Ref

Convert the Armadillo r8a7740 DT reference board support
to use shmobile_init_delay() to be able to migrate away
from per-SoC delay setup functions.

Signed-off-by: Magnus Damm <damm+renesas@opensource.se>
Tested-by: Geert Uytterhoeven <geert@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>