mesa: change state query return value for RGB565

mesa: change state query return value for RGB565

The GL_BGR and GL_UNSIGNED_SHORT_5_6_5_REV are not defined anywhere in
OpenGL ES 3.2 (or earlier) specification, and there are no known extensions
in the Khronos registry that would add these enums as valid responses for
glGetIntegerv(GL_IMPLEMENTATION_COLOR_READ_TYPE) and
glGetIntegerv(GL_IMPLEMENTATION_COLOR_READ_FORMAT) queries.

Note that this patch does not change the bit layout returned by the query. As
defined by the GL spec, the bit layout of GL_RGB + GL_UNSIGNED_SHORT_5_6_5 and
GL_BGR + GL_UNSIGNED_SHORT_5_6_5_REV are identical.

TEST=dEQP-GLES3.functional.state_query.integers.*

Signed-off-by: Haixia Shi <hshi@chromium.org>
Reviewed-by: Chad Versace <chadversary@chromium.org>
Reviewed-by: Jason Ekstrand <jason@jlekstrand.net>
Cc: Stéphane Marchesin <marcheu@chromium.org>
Change-Id: I81bbc8ccdc7e125edaeae443baf6fa8fdefcc6b6