i915: correctly parse/set the context flags

i915: correctly parse/set the context flags

With an earlier commit we've spit the flags parsing to a separate
function, but forgot to update all the dri modules to use it.

Noticed when we've enabled KHR_debug for every dri module - fdo#93048

Fixes: 38366c0c6e7 "dri_util: Don't assume __DRIcontext->driverPrivate
is a gl_context"
Cc: Mark Janes <mark.a.janes@intel.com>
Cc: "11.0 11.1" <mesa-stable@lists.freedesktop.org>
Cc: Kristian Høgsberg <krh@bitplanet.net>
Cc: Ian Romanick <ian.d.romanick@intel.com>
Signed-off-by: Emil Velikov <emil.l.velikov@gmail.com>
Reviewed-by: Mark Janes <mark.a.janes@intel.com>
Tested-by: Mark Janes <mark.a.janes@intel.com>
(cherry picked from commit 72fda2b710d864d23aec1e8f959147d05c5ff3f3)