ARM: shmobile: add R8A7778 basis support

Add initial support for the R8A7778 R-Car M1A SoC.
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.

It is based on v1.0 datasheet

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Acked-by: Magnus Damm <damm@opensource.se>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>