ARM: shmobile: Add r8a7790 SMP support using APMU code

Add r8a7790 SMP support using the shared APMU code. To enable
SMP the r8a7790 specific DTS needs to be updated to include
CPU cores, and this is happening in a separate patch.

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