intel: Refactor common platform code [1/5]

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
diff --git a/plat/intel/soc/agilex/include/agilex_pinmux.h b/plat/intel/soc/agilex/include/agilex_pinmux.h
index e6a7b34..fe01062 100644
--- a/plat/intel/soc/agilex/include/agilex_pinmux.h
+++ b/plat/intel/soc/agilex/include/agilex_pinmux.h
@@ -12,7 +12,7 @@
 #define AGX_PINMUX_PINMUX_EMAC0_USEFPGA	0xffd13300
 #define AGX_PINMUX_IO0_DELAY		0xffd13400
 
-#include "agilex_handoff.h"
+#include "socfpga_handoff.h"
 
 void config_pinmux(handoff *handoff);