intel: Delete devinfo->must_use_separate_stencil

This is used by a single place in ISL only for sanity checking the
decisions it has already made.  The knowledge is already all centralized
in ISL these days, so we don't need a device info bit.

Reviewed-by: Dylan Baker <dylan.c.baker@intel.com>
Reviewed-by: Lionel Landwerlin <lionel.g.landwerlin@intel.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/33764>
3 files changed