drm/i915/mtl: enable local stolen memory

drm/i915/mtl: enable local stolen memory

As an integrated GPU, MTL does not have local memory and HAS_LMEM()
returns false.  However the platform's stolen memory is presented via
BAR2 (i.e., the BAR we traditionally consider to be the GMADR on IGFX)
and should be managed by the driver the same way that local memory is
on dgpu platforms (which includes setting the "lmem" bit on page table
entries).  We use the term "local stolen memory" to refer to this
model.

The major difference from the traditional BAR2 (GMADR) is that
the stolen area is mapped via the BAR2 while in the former BAR2 is an
aperture into the GTT VA through which access are made into stolen area.

BSPEC: 53098, 63830

v2:
1. dropped is_dsm_invalid, updated valid_stolen_size check from Lucas
(Jani, Lucas)
2. drop lmembar_is_igpu_stolen
3. revert to referring GFXMEM_BAR as GEN12_LMEM_BAR (Lucas)

v3:(Jani)
1. rename get_mtl_gms_size to mtl_get_gms_size
2. define register for MMIO address

v4:(Matt)
1. Use REG_FIELD_GET to read GMS value
2. replace the calculations with SZ_256M/SZ_8M

v5: Include more details to commit message on how it is different from
earlier platforms (Anshuman)

Cc: Matt Roper <matthew.d.roper@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: CQ Tang <cq.tang@intel.com>
Signed-off-by: Aravind Iddamsetty <aravind.iddamsetty@intel.com>
Original-author: CQ Tang
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220929114658.145287-1-aravind.iddamsetty@intel.com