Change in coreboot[master]: soc/amd/cezanne: Add APCB integration code

[Bao Zheng (Code Review)]

Attention is currently required from: Jason Glenesk, Martin Roth, Marshall Dawson, Zheng Bao.
Bao Zheng has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/49737 )

Change subject: soc/amd/cezanne: Add APCB integration code
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Patch Set 11:

(2 comments)

Patchset:

PS11: 
This change has been merged to previous one.

File src/soc/amd/cezanne/Makefile.inc:

https://review.coreboot.org/c/coreboot/+/49737/comment/af99a159_6875e603 
PS11, Line 116: ifneq ($(APCB_SOURCES),)
              : OPT_PSP_APCB_FILES= --instance 0 --apcb $(APCB_SOURCES)
              : endif
              : ifneq ($(APCB_SOURCES_RECOVERY),)
              : OPT_PSP_APCB_FILES+= --instance 10 --apcb $(APCB_SOURCES_RECOVERY)
              : endif
              : ifneq ($(APCB_SOURCES_68),)
              : OPT_PSP_APCB_FILES+= --instance 18 --apcb $(APCB_SOURCES_68)
              : endif
> I dont know why this detection of empty string doesn't work. That causes the not booting issue.

Done.
The variable like APCB_SOURCES can not be surely propagated from Makefile to Makefile.
Use Kconfig option instead.