ARM: 7086/2: mach-integrator: modernize clock event registration

Drop mult, shift and delta calculations and let the
clockevent core scale this as appropriate.

Set the minimum interval to 1 rather than 15 (0xf), there
is nothing in the data sheets I have indicating that 15
should be some minimum value.

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>