ARM: shmobile: Break out R-Car SYSC PM code

Break out the R-Car SYSC power management code from
the r8a7779 SoC code. With this new shared R-Car SYSC
code base it is possible to hook in Generation 2 SoCs
as well.

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