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:

(1 comment)

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

https://review.coreboot.org/c/coreboot/+/49737/comment/4b2b5135_be58ef74 
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.