drm/i915/bios: Use the copy of the LFP data table always

drm/i915/bios: Use the copy of the LFP data table always

Currently get_lvds_fp_timing() still returns a pointer to the original
data block rather than our copy. Let's convert the data pointer offsets
to be relative to the data block rather than the whole BDB. With that
we can make get_lvds_fp_timing() return a pointer to the copy.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220405173410.11436-4-ville.syrjala@linux.intel.com
Reviewed-by: Jani Nikula <jani.nikula@intel.com>