Continuation of the effort to declutter i915_drv.h.

Also, component specific helpers which consult the iommu/virtualization
helpers moved to respective component source/header files as appropriate.

v2:
 * s/dev_priv/i915/ in intel_scanout_needs_vtd_wa. (Lucas)
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220329090204.2324499-1-tvrtko.ursulin@linux.intel.com
[tursulin: fixup conflict in i915_drv.h]