drm/i915/dsi: Move poking of panel-enable GPIO to intel_dsi_vbt.c

On some older devices (BYT, CHT) which may use v2 VBT MIPI-sequences,
we need to manually control the panel enable GPIO as v2 sequences do
not do this.

So far we have been carrying the code to do this on BYT/CHT devices
with a Crystal Cove PMIC in vlv_dsi.c, but as this really is a shortcoming
of the VBT MIPI-sequences, intel_dsi_vbt.c is a better place for this,
so move it there.

This is a preparation patch for adding panel-enable and backlight-enable
GPIO support for BYT devices where instead of the PMIC the SoC is used
for backlight control.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191216205122.1850923-3-hdegoede@redhat.com