drm/i915: Try to guess PCH type even without ISA bridge

Some vmm like hyperv and crosvm don't supply any ISA bridge to their guest,
when igd passthrough is equipped on these vmm, guest i915 display may
couldn't work as guest i915 detects PCH_NONE pch type.

When i915 runs as guest, this patch guess pch type through gpu type even
without ISA bridge.

v2: Fix CI warning
v3: Add HAS_DISPLAY()= true condition beforce guessing virt pch, then
    refactori.
v4: Fix CI warning

Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Co-developed-by: Xiong Zhang <xiong.y.zhang@intel.com>
Signed-off-by: Xiong Zhang <xiong.y.zhang@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210114005819.4290-1-xiong.y.zhang@intel.com