fbdev: sh_mipi_dsi: remove driver

Remove the sh_mipi_dsi driver as it appears to be unused since
c0bb9b30 ("ARCH: ARM: shmobile: Remove ag5evm board support").

Signed-off-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>