mesa/main: fix up _mesa_has_rg_textures for gles2

rg-textures are supported in GLES 2.0 if EXT_texture_rg, so let's make
sure the enums are accepted.

Fixes: 510b642460 "mesa/main: do not allow rg-textures enums before gles3"
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=108936
Signed-off-by: Erik Faye-Lund <erik.faye-lund@collabora.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>
Reviewed-by: Marek Olšák <marek.olsak@amd.com>

src/mesa/main/context.h

@@ -378,7 +378,8 @@ _mesa_has_packed_float(const struct gl_context *ctx)
 static inline bool
 _mesa_has_rg_textures(const struct gl_context *ctx)
 {
-   return _mesa_has_ARB_texture_rg(ctx) || _mesa_is_gles3(ctx);
+   return _mesa_has_ARB_texture_rg(ctx) || _mesa_has_EXT_texture_rg(ctx) ||
+          _mesa_is_gles3(ctx);
 }
 
 static inline bool