ARM: 7087/2: mach-integrator: get timer frequency from clock

We already have a clock definition for the 24MHz clock in
the Integrator, use that instead of some unclear defines
from the platform.h header. Also delete the senseless
comment that the file shouldn't be edited, I just edited it
and the world didn't come to an end, so it's obviously
false. If anyone still has the mentioned ".s file" and the
s2h awk script generating that header, raise your hand
(and give me your files).

Acked-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>