closes acidanthera/bugtracker#1717

E.g. specifying 0 (1MB) should reduce 8 GB BAR to 256 MB if 256 MB
BAR is the smallest supported BAR size.

This resolves the general set of compatibility issues with macOS 12
software updater, which requires T2 mac models to have T2 SB models.

This variable is derived from `SecureBootModel` specified in the config
(e.g. j137 becomes J137AP) and is used by macOS 12 during updates
and installations. Setting this variable allows to use macOS 12
with T2 board identifiers, e.g. j137.

Docs: Fix incorrect Drivers plist type dict->array; add 'Failsafe: Empty' where missing for other arrays

OpenLinuxBoot: Make user non-'+' options override everything including `root=`; include autodetect kernel opts lines in selectable verbose output.