ibmaem: update the documentation to reflect the current name

Minor documentation update to reflect the current full name of the power
management hardware interface and reflows the text a bit.

Signed-off-by: Darrick J. Wong <djwong@us.ibm.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>