drm/i915/bxt, glk: Give a proper name to the power well struct phy field

drm/i915/bxt, glk: Give a proper name to the power well struct phy field

Follow-up patches will add new fields to the i915_power_well struct that
are specific to the hsw_power_well_ops helpers. Prepare for this by
changing the generic 'data' field to a union of platform specific
structs.

Signed-off-by: Imre Deak <[email protected]>
Reviewed-by: Arkadiusz Hiler <[email protected]>
Link: https://patchwork.freedesktop.org/patch/msgid/[email protected]
Signed-off-by: Daniel Vetter <[email protected]>