mesa: fix errors when reading depth with glReadPixels

mesa: fix errors when reading depth with glReadPixels

OpenGL ES 3.0 spec 3.7.2 "Transfer of Pixel Rectangles" specifies
DEPTH_COMPONENT, UNSIGNED_INT as a valid couple, validation for
internal format is checked by is_float_depth().

Fix regression caused by 81d2fd91a90e5b2fd9fd74792a7a7c329f0e4d29 in:
   ES3-CTS.gtf.GL3Tests.packed_pixels.packed_pixels

Test uses GL_DEPTH_COMPONENT, UNSIGNED_INT only when GL_NV_read_depth
extension is present.

v2: change check in _mesa_error_check_format_and_type to be explicit
    for ES 2.0+, desktop OpenGL does not allow this behaviour + uses
    this function for both glReadPixels and glDrawPixels validation.
    (No Piglit regressions seen with v2.)

Signed-off-by: Tapani Pälli <tapani.palli@intel.com>
Reviewed-by: Anuj Phogat <anuj.phogat@gmail.com>
Reviewed-by: Samuel Iglesias Gonsálvez <siglesias@igalia.com> [v1]
Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=92009
Cc: "10.6 11.0" <mesa-stable@lists.freedesktop.org>