drivers: sh: Restrict INTC_USERIMASK to SH4A

register_intc_userimask() is called from sh4a code only.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Tested-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com> [r8a7779 legacy]
Signed-off-by: Simon Horman <horms+renesas@verge.net.au>