ARM: Show proper respect for Heinrich Hertz by using the correct unit for frequency

The SI unit of frequency is Hertz, named after Heinrich Hertz, and is
given the symbol "Hz" to denote this.  "hz" is not the unit of frequency,
and is in fact meaningless.

Fix arch/arm to correctly use "Hz", thereby acknowledging Heinrich Hertz'
contribution to the modern world.

Acked-by: Tony Lindgren <tony@atomide.com>
Acked-by: Robert Jarzmik <robert.jarzmik@free.fr>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>