drm/i915/dsi: Use devm_gpiod_get() for all GPIOs

soc_gpio_set_value() already uses devm_gpiod_get(), lets be consistent
and use devm_gpiod_get() for all GPIOs.

This allows removing the intel_dsi_vbt_gpio_cleanup() function,
which only function was to put the GPIO-descriptors.

Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Reviewed-by: Andy Shevchenko <andy@kernel.org>
Acked-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231201161130.23976-1-hdegoede@redhat.com