video: fbdev: sh_mobile_meram: Drop SUPERH platform dependency

Since commit a521422e ("ARM: shmobile: mackerel: Remove Legacy C
board code"), the only remaining platforms using this driver are SuperH
SH-Mobile SoCs (sh7723).  As both SUPERH and ARCH_SHMOBILE are set for
these platforms, the SUPERH dependency can be dropped.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>