ARM: 6159/1: Move IOP to use common mult/shift calculation code

Since the infrastructure for determining shift/mult values from a
clock rate and a minimum programmable rate is now in the kernel,
lets remove this custom code.

Cc: Deepak Saxena <dsaxena@plexity.net>
Acked-by: Mikael Pettersson <mikpe@it.uu.se>
Signed-off-by: Linus Walleij <linus.walleij@stericsson.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>