drm/i915: switch i915 core to generic VLV IOSF SB functions

drm/i915: switch i915 core to generic VLV IOSF SB functions

We'll want to relocate the unit specific functions to display, making
them inaccessible to i915 core. As there aren't that many users in i915
core, we can just convert them to the generic VLV IOSF SB read/write
functions.

v2: Use BIT(unit) for get/put

Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://lore.kernel.org/r/3162c8768eeeba928bbc3d4aa2ddfc6a1030a451.1747061743.git.jani.nikula@intel.com
Signed-off-by: Jani Nikula <jani.nikula@intel.com>