dispatch: Make a header to go along with querymatrix.c.

dispatch: Make a header to go along with querymatrix.c.

This patch creates a header querymatrix.h, to allow functions defined
in querymatrix.c to be used from other .c files.  It also switches
from the nonstandard GL_APIENTRY to GLAPIENTRY.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>
v2: Don't declare _mesa_Get{Integer,Float}v in querymatrix.c.
Instead, just include main/get.h.

Reviewed-by: Chad Versace <chad.versace@linux.intel.com>