MAINTAINERS: update i915 and xe entries for include/drm/intel

MAINTAINERS: update i915 and xe entries for include/drm/intel

With all the Intel specific drm files under include/drm/intel, update
the i915, xe, and the shared display entries. Do not discriminate based
on file name pattern, just add the entire directory for all three
entries.

Cc: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Oded Gabbay <ogabbay@kernel.org>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Thomas Hellström <thomas.hellstrom@linux.intel.com>
Cc: Tvrtko Ursulin <tursulin@ursulin.net>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Acked-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/e0fdf28307bb3e457d8c67966c09c44cf7ff5783.1717075103.git.jani.nikula@intel.com