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

[Yu-Ping Wu (Code Review)]

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

Change subject: lib: Add fls support
......................................................................

Patch Set 3: Code-Review+1

(2 comments)

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

https://review.coreboot.org/c/coreboot/+/59738/comment/13712305_b8f00d33 
PS1, Line 129: ARCH_X86
> We should use […]

So, will the latest patchset cause problems on x86 platforms?

https://review.coreboot.org/c/coreboot/+/59738/comment/073a2b7e_2ff2ca82 
PS1, Line 137: fls
> Please add unit tests. See CB:56543 as an example.

It would still be nice to provide unit tests.