arm: socfpga: Move Stratix10 and Agilex clock manager common code

Move duplicated function cm_get_qspi_controller_clk_hz to clock_manager.c.

Signed-off-by: Siew Chin Lim <elly.siew.chin.lim@intel.com>
Signed-off-by: Tien Fong Chee <tien.fong.chee@intel.com>
Reviewed-by: Ley Foon Tan <ley.foon.tan@intel.com>