clk: socfpga: Map the clk manager base address in the clock driver

The clk manager's base address was being mapped in SOCFPGA's arch code and
being extern'ed out to the clock driver. This method is not correct, and the
arch code was not really doing anything with that clk manager anyways.

This patch moves the mapping of the clk manager's base address in the clock
driver itself. Cleans up CLK_OF_DECLARE() into a single registration of all
the clocks.

Suggested-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Dinh Nguyen <dinguyen@altera.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
---
v2: Use a static declaration for the clk_mgr_base_addr. Clean up the
    CLK_OF_DECLARE() as suggested by Arnd.