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