drm/i915: include linux/highmem.h and linux/swap.h where needed

Include linux/highmem.h and linux/swap.h explicitly where needed so we
can drop the linux/i2c.h include from i915_drv.h where it pulled in the
dependencies implicitly.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220303181931.1661767-5-jani.nikula@intel.com