Modify of_clk_init function so that it will determine which
driver to initialize based on device tree instead of each driver
registering to it.

Based on a similar patch for drivers/irqchip by Thomas Petazzoni and
drivers/clocksource by Stephen Warren.
Signed-off-by: NPrashant Gaikwad <pgaikwad@nvidia.com>
Tested-by: NTony Prisk <linux@prisktech.co.nz>
Tested-by: NPawel Moll <pawel.moll@arm.com>
Tested-by: NRob Herring <rob.herring@calxeda.com>
Tested-by: NJosh Cartwright <josh.cartwright@ni.com>
Reviewed-by: NJosh Cartwright <josh.cartwright@ni.com>
Acked-by: NMaxime Ripard <maxime.ripard@anandra.org>
Signed-off-by: NMike Turquette <mturquette@linaro.org>
[mturquette@linaro.org: merge conflict from missing CLKSRC_OF_TABLES()]
Signed-off-by: NMike Turquette <mturquette@linaro.org>