mesa: In helpers, only check driver capability for meta

mesa: In helpers, only check driver capability for meta

Make API context and version checks done by the helper functions pass
unconditionally while meta is in progress. This transparently makes
extension checks solely dependent on struct gl_extensions while in meta.

v2: Use an 8-bit data type instead of a GLuint

Signed-off-by: Nanley Chery <nanley.g.chery@intel.com>
Reviewed-by: Chad Versace <chad.versace@intel.com>