Platform handoff structure no longer includes boot source selection.
Hence, those settings can now be configured through socfpga_plat_def.h.

Signed-off-by: Hadi Asyrafi <muhammad.hadi.asyrafi.abdul.halim@intel.com>
Change-Id: If7ec6a03bb25156a6670ebf8f77105c370b553f6

Pull out handoff driver to intel/soc/ common directory as they can be
shared by both Agilex and Stratix10 platform.

Share platform_def header between both Agilex and Stratix10 and store
platform specific definitions in socfpga_plat_def.h

Signed-off-by: Hadi Asyrafi <muhammad.hadi.asyrafi.abdul.halim@intel.com>
Change-Id: I8eff1afd7ee71704a36a54fad732ede4f557878d