[M] Change in coreboot[main]: drivers/intel/dtbt: Add discrete Thunderbolt driver

[Tim Crawford (Code Review)]

Attention is currently required from: Kyösti Mälkki, Martin L Roth, Michał Żygowski, Paul Menzel, Tim Wawrzynczak, Utkarsh H Patel.

Tim Crawford has posted comments on this change by Tim Crawford. ( https://review.coreboot.org/c/coreboot/+/75286?usp=email )

Change subject: drivers/intel/dtbt: Add discrete Thunderbolt driver
......................................................................

Patch Set 10:

(1 comment)

File src/drivers/intel/dtbt/dtbt.c:

https://review.coreboot.org/c/coreboot/+/75286/comment/bdbfac3a_bd60ed3b?usp... :
PS5, Line 187: 	printk(BIOS_DEBUG, "DTBT get security level\n");
> maybe add a comment here about why you need to get the security level before and after writing the s […]

This appears to have been just not implementing the required steps when changing the level. I think the intent is:

- `GET_SECURITY_LEVEL` to check if it needs to change in the first place
- `SET_SECURITY_LEVEL` to apply the desired security level (SL0 in this case)
- `GET_SECURITY_LEVEL` to verify controllers made the change, and rollback any changes if it failed

Without any of the checking, only the `SET_SECURITY_LEVEL` makes sense to keep here.