BCM2708: Migrate to the Common Clock Framework

As part of moving towards using Device Tree, the Common Clock Framework
has to be used instead of the BCM2708 clock implementation.

Selecting COMMON_CLK removes the need to set CLKDEV_LOOKUP and HAVE_CLK explicitly.

CONFIG_ARCH_BCM2708_CHIPIT #ifdef's are removed. They are no longer in use.

Signed-off-by: Noralf Tronnes <notro@tronnes.org>