ARM: davinci_all_defconfig: enable dumb vga-dac drm bridge

This enables the dumb-vga-dac driver by default for davinci boards.

The driver is needed for tilcdc support on da850-lcdk board.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>