arm: socfpga: Restructure Stratix10 and Agilex handoff code

Restructure Stratix10 and Agilex handoff code to used by
all SOC64 devices, in preparation to support handoff for
Diamond Mesa.

Remove wrap_pinmux_config_s10.c. Add wrap_handoff_soc64.c
which contains the generic function to parse the handoff
data.

Update system_manager_soc64.c to use generic handoff
function in wrap_handoff_soc64.c.

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