ARM: socfpga: clk: Obtain handoff base clock via DM

ARM: socfpga: clk: Obtain handoff base clock via DM

Bind fixed clock driver to the base clock instantiated in the handoff
DT and use DM clock framework to get their clock rate. This replaces
the ad-hoc DT parsing present thus far.

Signed-off-by: Marek Vasut <marex@denx.de>
Cc: Chin Liang See <chin.liang.see@intel.com>
Cc: Dinh Nguyen <dinguyen@kernel.org>
Cc: Ley Foon Tan <ley.foon.tan@intel.com>