soc: renesas: rcar-sysc: Add r8a774a1 support

Add support for RZ/G2M (R8A774A1) SoC power areas to the R-Car SYSC
driver.

Signed-off-by: Biju Das <biju.das@bp.renesas.com>
Reviewed-by: Chris Paterson <chris.paterson2@renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>