[S] Change in coreboot[master]: Makefile.inc: add signing procedure for power9 SoC

[Michał Żygowski (Code Review)]

Attention is currently required from: Krystian Hebel, Martin L Roth, Sergii Dmytruk.

Michał Żygowski has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/67066?usp=email )

Change subject: Makefile.inc: add signing procedure for power9 SoC
......................................................................

Patch Set 8:

(2 comments)

File Makefile.inc:

https://review.coreboot.org/c/coreboot/+/67066/comment/392411b4_d4f279be :
PS8, Line 1176: $(SBSIGNTOOLS
This is POWER9 specific right? We could omit compilation of this tool on other architectures which do not need this tool.

File src/soc/ibm/power9/Makefile.inc:

https://review.coreboot.org/c/coreboot/+/67066/comment/8538bcc9_8c8284fb :
PS8, Line 16: sign_and_add_ecc: $(obj)/coreboot.rom
I think we could extend the build_complete job like this:

build_complete:: $(SBSIGNTOOLS)

That way we can avoid compiling SBSIGNTOOLS for each architecture. All we need to do is to produce ECCed bootblock and signing keys at the ned of coreboot build process right?