drm/i915: Replace intel_bios_is_lspcon_present() with intel_bios_encoder_is_lspcon()

We always have encoder->devdata available on the platforms
that can have LSPCON. So let's start looking there instead
of digging it out from vbt.ports[].

And let's rename the function to fit the common pattern
for these things.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230208015508.24824-4-ville.syrjala@linux.intel.com


Reviewed-by: Jani Nikula <jani.nikula@intel.com>