drm/i915/reg: move pick even and pick to reg defs

This is a more logical place for generic helpers.

Cc: Lucas De Marchi <lucas.demarchi@intel.com>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/623327aee73a515300d99c8d65552ca92f3f0721.1668008071.git.jani.nikula@intel.com