drm/i915: Invoke another _DSM to enable MUX on HP Workstation laptops

On HP Fury G7 Workstations, graphics output is re-routed from Intel GFX
to discrete GFX after S3. This is not desirable, because userspace will
treat connected display as a new one, losing display settings.

The expected behavior is to let discrete GFX drives all external
displays.

The platform in question uses ACPI method \_SB.PCI0.HGME to enable MUX.
The method is inside the another _DSM, so add the _DSM and call it
accordingly.

I also tested some MUX-less and iGPU only laptops with that _DSM, no
regression was found.

v4:
 - Rebase.
 - Change the DSM name to avoid confusion.
 - Move the function call to intel_opregion.

v3:
 - Remove BXT from names.
 - Change the parameter type.
 - Fold the function into intel_modeset_init_hw().

v2:
 - Forward declare struct pci_dev.

Closes: https://gitlab.freedesktop.org/drm/intel/-/issues/3113
References: https://lore.kernel.org/intel-gfx/1460040732-31417-4-git-send-email-animesh.manna@intel.com/
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210520065832.614245-1-kai.heng.feng@canonical.com