drm/i915/pch: clean up includes

We no longer need i915_drv.h in intel_pch.c, and we no longer need
intel_pch.h universally.

With intel_pch.h being included from intel_display_core.h, it's still
included pretty much everywhere, but there's no need to include it
explicitly from i915_drv.h or xe_device_types.h.

Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://lore.kernel.org/r/68ec70f6880b7af19bc93b9817959299634a555d.1744364975.git.jani.nikula@intel.com


Signed-off-by: Jani Nikula <jani.nikula@intel.com>