clk: pxa: add pxa3xx clock driver

Move pxa25x clock drivers from arch/arm/mach-pxa to driver/clk.
In the move :
 - convert to new clock framework legacy clocks
 - provide clocks as before for platform data based boards
 - provide clocks through devicetree with clk-pxa-dt

Signed-off-by: Robert Jarzmik <robert.jarzmik@free.fr>
Signed-off-by: Michael Turquette <mturquette@linaro.org>