northbridge/intel/x4x: clean up includes

- Don't redefine D0F0_PCIEXBAR_LO, use the #define in x4x.h
- Move TPMBASE and TPM32() definitions into iomap.h
- Use "" style include for x4x.h in nortbridge files.
- Move includes of .h files out of x4x.h and into the c files that need
them.
- Protect function definitions in bootblock.

Change-Id: I3fdb579235c5446733a0ffba05fffe1a73381251
Signed-off-by: Martin Roth <martinroth@google.com>
Reviewed-on: https://review.coreboot.org/12849
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/northbridge/intel/x4x/raminit.c

@@ -22,7 +22,9 @@
 #include <delay.h>
 #include <halt.h>
 #include <lib.h>
-#include <northbridge/intel/x4x/x4x.h>
+#include "iomap.h"
+#include <southbridge/intel/i82801gx/i82801gx.h> /* smbus_read_byte */
+#include "x4x.h"
 #include <pc80/mc146818rtc.h>
 #include <spd.h>
 #include <string.h>