ARM: shmobile: Add shared EMEV2 code for ->init_machine()

Add a SoC specific function that initializes
clocks and starts DT probing in case of EMEV2.

This EMEV2 SoC support code may be built for
either legacy SHMOBILE or SMOBILE_MULTI.

The change allows us to support existing board
specific KZM9D DTB with these SoC specific
DT_MACHINE_START() callbacks.

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