FROMGIT: drm/i915/display: Cleanup intel_phy_is_combo()

Cleanup the intel_phy_is_combo
to accommodate for cases where combo phy is not available.

v2: retain comment that explains DG2 returning false from
intel_phy_is_combo() (Arun)

Cc: Arun R Murthy <arun.r.murthy@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Arun R Murthy <arun.r.murthy@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220725225028.98612-1-anusha.srivatsa@intel.com
(cherry picked from commit ace98ffc
 https://anongit.freedesktop.org/git/drm-intel.git

 drm-intel-next)

BUG=b:242077859
TEST=i915 driver loaded successfully

Change-Id: I29d71e641eee0a3b29c1c7a3af541c86a5de111f
Signed-off-by: Mohanram Meenakshisundaram <mohanram.meenakshisundaram@intel.com>
Reviewed-on: https://chromium-review.googlesource.com/c/chromiumos/third_party/kernel/+/3910570


Reviewed-by: Rajat Jain <rajatja@google.com>
Commit-Queue: Rajat Jain <rajatja@google.com>
Reviewed-by: Drew Davenport <ddavenport@chromium.org>
Tested-by: Rajat Jain <rajatja@google.com>