ARM: shmobile: Allow r8a7791 to build non-SMP APMU code

Build the APMU for r8a7791 even though SMP is
disabled in the kernel config. Also initialize
Suspend-to-RAM from pm-r8a7791.c to in the future
cover both UP and SMP use cases of the APMU.

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