drm/i915/bios: Get access to the tail end of the LFP data block

We need to start parsing stuff from the tail end of the LFP data block.
This is made awkward by the fact that the fp_timing table has variable
size. So we must use a bit more finesse to get the tail end, and to
make sure we allocate enough memory for it to make sure our struct
representation fits.

v2: Rebase due to the preallocation of BDB blocks
v3: Rebase due to min_size WARN relocation
v4: Document BDB_LVDS_LFP_DATA vs. BDB_LVDS_LFP_DATA_PTRS order (Jani)

Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220504150440.13748-4-ville.syrjala@linux.intel.com