drm: shmobile: remove unused MERAM support

Since commit a521422e  ("ARM: shmobile: mackerel: Remove Legacy C
board code") MERAM functionality is unused. Remove it.

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