mesa: add NV_image_formats extension support

mesa: add NV_image_formats extension support

This extension can be enabled automatically as it is a subset of
ARB_shader_image_load_store.

v2: Replace helper function by qualifier struct field (Ilia)
    Enable NV_image_formats using ARB_shader_image_load_store (Ilia)

v3: Drop extension field from gl_extensions (Ilia)
    Release notes (Ilia)

Signed-off-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=98480
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>