Change in coreboot[master]: mb/google/volteer/baseboard: Configure chipset_lockdown seperately

[Felix Singer (Code Review)]

Attention is currently required from: Furquan Shaikh, Tim Wawrzynczak, Angel Pons.
 Felix Singer has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/56209 )

Change subject: mb/google/volteer/baseboard: Configure chipset_lockdown seperately
......................................................................

Patch Set 2:

(1 comment)

Commit Message:

https://review.coreboot.org/c/coreboot/+/56209/comment/44f6a87a_ba3c0f2d 
PS2, Line 15: 
            : Thus, move `chipset_lockdown` out of `common_soc_config` in the
            : baseboard devicetree and configure it seperately.
            :
> It should be a Kconfig. And default to CHIPSET_LOCKDOWN_COREBOOT.

My initial idea was to swap the two enum values in `soc/intel/common/block/include/intelblocks/cfg.h`, that `CHIPSET_LOCKDOWN_COREBOOT` becomes 0 and thus the default, but that requires all boards using this setting or we need to identify the boards where `CHIPSET_LOCKDOWN_FSP` should be used.

We discussed this in IRC yesterday. Other possible options would be just dropping `CHIPSET_LOCKDOWN_FSP` and enforcing `CHIPSET_LOCKDOWN_COREBOOT` or replacing the devicetree option by a Kconfig option, as Angel mentioned.