Improve support of OpenGL for BeagleBone Black

Make ti-gfx working on BeagleBone Black by adding an ugly necessary
patch to the kernel wich fix:
pvrsrvkm: Unknown symbol v7_dma_map_area
pvrsrvkm: Unknown symbol v7_dma_flush_range

Add drivers to the default kernel config used in beaglebone_defconfig
to enable the framebuffer.

Signed-off-by: Hadrien Boutteville <hadrien.boutteville@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>