drm/i915/pci: move intel_pci_config.h under include/drm/intel

drm/i915/pci: move intel_pci_config.h under include/drm/intel

Since the PCI registers are used from both i915 display and core, move
intel_pci_config.h to include/drm/intel/pci_config.h. Drop the intel_
prefix from the name to reduce tautology.

With this, we can drop the corresponding xe display compat header.

v2: Rebase

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patch.msgid.link/5aac6c711c3f0a09fc52f322455a4a4b35f80a82.1775590536.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>