drm/i915/tgl: Simply subplatform detection

In the past we had a need to differentiate TGL U and TGL Y, there
was a different voltage swing table for each subplatform and some PCI
ids of this subplatforms are shared but it turned out that it was a
specification mistake and the voltage swing table was indeed the same
but we went ahead with that patch because we needed to differentiate
TGL U and Y from TGL H and by that time TGL H was embargoed so that
was the perfect way to land it upstream.

Now the embargo for TGL H is long past and now we even have
INTEL_TGL_12_GT1_IDS with all TGL H ids, so we can drop this PCI root
check and only rely in the PCI ids to differentiate TGL U and Y from
TGL H that actually has code differences.

Besides the simplification this will fix issues in virtualization
environments where the PCI root is virtualized and don't have the same
id as actual hardware.

v2:
- add and set INTEL_SUBPLATFORM_UY

Cc: Fred Gao <fred.gao@intel.com>
Cc: Tvrtko Ursulin <tvrtko.ursulin@linux.intel.com>
Signed-off-by: José Roberto de Souza <jose.souza@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Tested-by: Yu He <yu.he@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220222141424.35165-1-jose.souza@intel.com