ARM: shmobile: defconfig: Restore graphical consoles

As of commit f611b1e7 ("drm: Avoid circular dependencies for
CONFIG_FB"), CONFIG_FB is no longer auto-enabled.  While CONFIG_FB may
be considered unneeded for systems where graphics is provided by a DRM
driver, R-Mobile A1 still relies on a frame buffer device driver for
graphics support.

Restore support for graphics on R-Mobile A1 and graphical consoles on
DRM-based systems by explicitly enabling CONFIG_FB in the defconfig for
Renesas ARM systems.

Fixes: f611b1e7

 ("drm: Avoid circular dependencies for CONFIG_FB")
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/2a4474be1d2c00c6ca97c2714844ea416a9ea9a9.1626084948.git.geert+renesas@glider.be