drm/i915: convert vlv_dpio_read()/write() from pipe to phy

vlv_dpio_read() and vlv_dpio_write() really operate on the phy, not
pipe. Passing the pipe instead of the phy as parameter is supposed to be
a convenience, but when the caller has the phy, it becomes an
inconvenience. See e.g. chv_dpio_cmn_power_well_enable() and
assert_chv_phy_powergate().

Figure out the phy in the callers, and pass phy to the dpio functions.

v2: retract one overzealous pipe->phy change (Ville)

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/20231114104534.4180144-3-jani.nikula@intel.com