[ARM] 5437/1: Add documentation for "nohlt" kernel parameter

As per discussion in:
http://marc.info/?l=linux-arm-kernel&m=123633652517391&w=2



Signed-off-by: Paulius Zaleckas <paulius.zaleckas@teltonika.lt>
Acked-by: Paul Mundt <lethal@linux-sh.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>