clk: socfpga: build together Stratix 10, Agilex and N5X clock drivers

On a multiplatform kernel there is little benefit in splitting each
clock driver per platform because space savings are minimal.  Such split
also complicates the code, especially after adding compile testing.

Build all arm64 Intel SoCFPGA clocks together with one entry in
Makefile.  This also removed duplicated line in the Makefile (selecting
common part of clocks per platform).

Signed-off-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Dinh Nguyen <dinguyen@kernel.org>