Change in coreboot[master]: lib: Add fls support

[Jianjun Wang (Code Review)]

Attention is currently required from: Hung-Te Lin, Shelley Chen, Paul Menzel, Julius Werner, Yu-Ping Wu.
Jianjun Wang has posted comments on this change. ( https://review.coreboot.org/c/coreboot/+/59738 )

Change subject: lib: Add fls support
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Patch Set 3:

(2 comments)

File src/commonlib/bsd/include/commonlib/bsd/helpers.h:

https://review.coreboot.org/c/coreboot/+/59738/comment/d3c56c2f_18919617 
PS1, Line 129: ARCH_X86
> So, will the latest patchset cause problems on x86 platforms?

I only have the environment for cherry board, and have no idea how to build for x86 platform, could you please provide some suggestions?

https://review.coreboot.org/c/coreboot/+/59738/comment/2ae09955_2bd01f4d 
PS1, Line 137: fls
> It would still be nice to provide unit tests.

Sure, is there any document can tell how to do the unit tests?