mainboard_vbt_filename() in src/mainboard/lenovo/x200/blc.c does not work as intended
Date back to coreboot 4.9, mainboard_vbt_filename() in src/mainboard/lenovo/x200/blc.c calls get_blc_pwm_freq_value(NULL), making the following if condition always falling to the first, not to mention null dereference on strcmp() in get_blc_pwm_freq_value().
In order to determine the correct vbt filename at runtime, edid ascii string should be obtained first.
This issue may be distantly related to #474.
This is going to be fixed with https://review.coreboot.org/c/coreboot/+/74181 .