ARM: shmobile: defconfig: Switch to DRM_SHMOBILE

Now the DRM driver for the SH-Mobile LCD Controller supports DT, replace
the legacy frame buffer device driver by the DRM driver.

Disable frame buffer device drivers, as this was the last frame buffer
device driver for Renesas ARM systems.
Enable CONFIG_DRM_FBDEV_EMULATION and CONFIG_FB_DEVICE, as these are no
longer auto-enabled since commit bb6c4507

 ("drm: fix up fbdev
Kconfig defaults").

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/3d17d8418ddabeb84ff5fa1cdd16439ddc84286f.1700669207.git.geert+renesas@glider.be