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/mainboard/google/gru/romstage.c

@@ -19,6 +19,7 @@
 #include <arch/exception.h>
 #include <arch/mmu.h>
 #include <cbfs.h>
+#include <cbmem.h>
 #include <console/console.h>
 #include <program_loading.h>
 #include <romstage_handoff.h>
@@ -28,6 +29,7 @@
 #include <soc/sdram.h>
 #include <symbols.h>
 #include <soc/usb.h>
+#include <stdlib.h>
 
 #include "pwm_regulator.h"