drm/i915/vbt: Parse panel options separately from timing data

Newer VBT versions will add an alternate way to read panel DTD
information, so let's split parsing of the general panel information
from the timing data in preparation.

Cc: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>
Reviewed-by: Jesse Barnes <jsbarnes@google.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191115165132.9472-2-matthew.d.roper@intel.com