gbm: dlopen libglapi so gbm_create_device works

gbm: dlopen libglapi so gbm_create_device works

Dri driver libs are not linked to pull in libglapi so gbm_create_device()
fails when it tries to dlopen them (unless the application is linked
with something that does pull in libglapi, like libGL).
Until dri drivers can be fixed properly, dlopen libglapi before trying
to dlopen them.

Cc: "10.5 10.6" <mesa-stable@lists.freedesktop.org>
Signed-off-by: Frank Henigman <fjhenigman@google.com>
[Emil Velikov: Drop misleading bugzilla link, mention that libname differs]
Reviewed-by: Emil Velikov <emil.l.velikov@gmail.com>