Add support for the ARM, AHB, APB and DDR clocks found on the
WM8505, WM8650, WM8750 and WM8850 SoCs.

These clocks are gateable, but the enable part of the clock definition
is left out as there are no users for these clocks, and we don't want
them being disabled at boot, but it does provide users the ability to
check the current rate of these clocks.
Signed-off-by: Tony Prisk <linux@prisktech.co.nz>