Documentation: Update mmiotrace.txt

Fix typos, spellos, hyphenation, line lengths.

BTW:  are there some userspace tools?  There is a reference to
some at the wiki page, but there are no tools listed there.

Signed-off-by: Randy Dunlap <randy.dunlap@oracle.com>
Acked-by: Pekka Paalanen <pq@iki.fi>
LKML-Reference: <4B2C0D68.6080401@oracle.com>
Signed-off-by: Ingo Molnar <mingo@elte.hu>