x86, UV: Modularize BAU send and wait

Streamline the large uv_flush_send_and_wait() function by use of
a couple of helper functions.

And remove some excess comments.

Signed-off-by: Cliff Wickman <cpw@sgi.com>
Cc: gregkh@suse.de
LKML-Reference: <E1OJvNy-0004ay-IH@eag09.americas.sgi.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>