drm/i915: move INTEL_FRONTBUFFER_* macros to intel_frontbuffer.h

The macros clearly don't belong in i915_drv.h. Move to
intel_frontbuffer.h.

Also split the BUILD_BUG_ON()s to intel_frontbuffer_track() to avoid
depending on some other macros in the header.

Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Reviewed-by: Lucas De Marchi <lucas.demarchi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/c899fd1ef2220564a876cd88c03e53c4c7b0168b.1661346845.git.jani.nikula@intel.com