drm/i915/dpio: Clean up the vlv/chv PHY register bits

Use REG_BIT() & co. for the vlv/chv DPIO PHY registers.

Note that DPIO_BIAS_CURRENT_CTL_SHIFT was incorrectly defined
to be 21 wheres 20 is the correct value. It is not used in the
code though so didn't bother splitting to a separate patch.

v2: drop stray tabs (Jani)

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240422083457.23815-14-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>