ARM: omap2plus_defconfig: update display configs

omapfb and omapdrm were recently made independent of each other, and
this required Kconfig option changes. This patch changes the
omap2plus_defconfig to enable display similarly as before: omapfb and
panel & encoder drivers as modules.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>