Change in coreboot[master]: lib: Add __fls() (Find Last Set)

[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() (Find Last Set)
......................................................................

Patch Set 5:

(2 comments)

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

https://review.coreboot.org/c/coreboot/+/59738/comment/802389c8_a230fb49 
PS1, Line 129: ARCH_X86
> So, there are still errors for PS4 (see Jenkins build console): […]

Done

https://review.coreboot.org/c/coreboot/+/59738/comment/c08d7228_5a591f0d 
PS1, Line 137: fls
> I've created the unit tests for lib.h in CB:59834. Feel free to rebase this on top of that.

I just add it as the alias for log2(), do we still need to add unit tests in this case.