rpb-wayland.conf: add libgbm PREFERRED_PROVIDERs for TI's omap-a15
rpb-wayland.conf: add libgbm PREFERRED_PROVIDERs for TI's omap-a15

Signed-off-by: Andrey Konovalov <6decb425dd3212bf9b96628630c2d12a43fdad79@linaro.org>

96boards/meta-rpb,fboudra/meta-rpb,fboudra/meta-rpb,fboudra/meta-rpb,96boards/meta-rpb