drm/i915: Add 16bit register/mask operators

Add the support macros to define/extract bits as 16bits.

v2: checkpatch fixes
Reviewed-by: Gustavo Sousa <gustavo.sousa@intel.com>
Signed-off-by: Clint Taylor <clinton.a.taylor@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230515231725.3815199-2-clinton.a.taylor@intel.com