Add support for the A3SG power domain, and hook it up as a subdomain of
A4S.
This domain contains the SGX540 hardware block, which is currently not
used by any driver.
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be> Signed-off-by: Simon Horman <horms+renesas@verge.net.au>