clk: pxa: declare init function and data __init

As the clock descriptions are constant and only usefull at init time,
mark them as such by :
 - spliting clock description (desc) and clock private data (dynamic)
 - mark __initdata clock descriptions

This makes all the register and descriptions of the clocks to go after
kernel init phase.

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