drm/xe/pf: Assert LMEM provisioning is done only on DGFX

The Local Memory (aka VRAM) is only available on DGFX platforms.
We shouldn't attempt to provision VFs with LMEM or attempt to
update the LMTT on non-DGFX platforms. Add missing asserts that
would enforce that and fix release code that could crash on iGFX
due to uninitialized LMTT.

Fixes: c063cce7 ("drm/xe/pf: Update the LMTT when freeing VF GT config")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Piotr Piórkowski <piotr.piorkowski@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240607153155.1592-1-michal.wajdeczko@intel.com