drm/i915/dg2: Add SQIDI steering

drm/i915/dg2: Add SQIDI steering

Although DG2_G10 platforms will always have all SQIDI's present and
don't need steering for registers in a SQIDI MMIO range, this isn't true
for DG2_G11 platforms; only SQIDI's 2 and 3 can be used on those.

We handle SQIDI ranges a bit differently from other types of explicit
steering.  The SQIDI ranges belong to either the MCFG unit or the SF
unit, both of which have their own dedicated steering registers and do
not use the typical 0xFDC steering control that all other types of
ranges use.  Thus we only need to worry about picking a valid initial
value for the MCFG and SF steering registers (0xFD0 and 0xFD8
respectively) at driver init; they won't change after we set them up so
we don't need to worry about re-steering them explicitly at runtime.

Given that any SQIDI value should work fine for DG2-G10 and XeHP SDV,
while only values of 2 and 3 are valid for DG2-G11, we'll just
initialize the MCFG and SF steering registers to a constant value of "2"
for all XeHP-based platforms for simplicity --- that will work in all
cases.

Bspec: 66534
Cc: Radhakrishna Sripada <radhakrishna.sripada@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210729170008.2836648-6-matthew.d.roper@intel.com