lib: put romstage_handoff implementation in own compilation unit

Instead of putting all the functions inline just put the
current implementation into a C file. That way all the implementation
innards are not exposed.

Lastly, fix up the fallout of compilation units not including the
headers they actually use.

Change-Id: I01fd25d158c0d5016405b73a4d4df3721c281b04
Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-on: https://review.coreboot.org/17648
Tested-by: build bot (Jenkins)
Reviewed-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/drivers/intel/fsp1_1/romstage.c

@@ -34,6 +34,7 @@
 #include <smbios.h>
 #include <soc/intel/common/mrc_cache.h>
 #include <stage_cache.h>
+#include <string.h>
 #include <timestamp.h>
 #include <tpm.h>
 #include <vendorcode/google/chromeos/chromeos.h>