ARM: socfpga: Upgrade clk driver for socfpga to make use of dts clock entries

With this patch, the socfpga clk driver is able to query the clock and clock
rates appropriately.

Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Reviewed-by: Pavel Machek <pavel@denx.de>
Signed-off-by: Olof Johansson <olof@lixom.net>