gbm: convert gbm bo format to fourcc format on dma-buf import

gbm: convert gbm bo format to fourcc format on dma-buf import

At the moment if a gbm buffer is imported and the gbm buffer
has an old-style GBM_BO_FORMAT format, the import will crash,
since it's passed directly to DRI functions that expect
a fourcc format (as provided by the newer GBM_FORMAT
definitions)

This commit addresses the problem in two ways:

1) it prevents invalid formats from leading to a crash by
returning EINVAL if the image couldn't be created

2) it translates GBM_BO_FORMAT formats into the comparable
GBM_FORMAT formats.

Reference: https://bugzilla.gnome.org/show_bug.cgi?id=753531
CC: "10.6 11.0" <mesa-stable@lists.freedesktop.org>
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Kristian Høgsberg <krh@bitplanet.net>