dri: add missing 16bits formats mapping

dri: add missing 16bits formats mapping

i965 advertises the 16-bit R and RG formats through
eglQueryDmaBufFormatsEXT but falls over when a client tries to use or
asks more information about such a format because
driImageFormatToGLFormat returns MESA_FORMAT_NONE.

Found by Eero Tamminen.

v2: Add G16R16 formats (Lionel)

v3: Fix G16R16 mapping to mesa format (Jason)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106642
Reviewed-by: Plamena Manolova <plamena.manolova@intel.com> (v2)
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>