ARM: shmobile: Initial r7s72100 SoC support

Add initial support for the r7272100 SoC including:
 - Single Cortex-A9 CPU Core
 - GIC

No static virtual mappings are used, all the components
make use of ioremap(). DT_MACHINE_START is still wrapped
in CONFIG_USE_OF to match other mach-shmobile code.

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