[PATCH]: powerpc documentation: Clarify why twi appears in the i/o macros.

[Paul Mackerras]

Linas Vepstas writes:

> Clarify why twi appears in the i/o macros. Shorten some over-length
> lines, while we're at it.

[snip]

> + * A data-dependent branch followed by an isync ensures that no

I think it's potentially confusing to talk about data-dependent
branches when what the code does is a twi instruction.  Even if you
argue that a twi is a data-dependent branch (and I disagree with that,
since a trap is not a branch), that wouldn't be obvious to a casual
reader of the code.  In other words, I don't think the comment
clarifies the situation very much.

Paul.