device/smbus_host: Declare common early SMBus prototypes

Change-Id: I1157cf391178a27db437d1d08ef5cb9333e976d0
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/38233
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Angel Pons <th3fanbus@gmail.com>

src/northbridge/intel/x4x/raminit.c

@@ -1,15 +1,11 @@
 /* SPDX-License-Identifier: GPL-2.0-or-later */
 
 #include <device/pci_ops.h>
+#include <device/smbus_host.h>
 #include <cbmem.h>
 #include <cf9_reset.h>
 #include <console/console.h>
 #include <arch/cpu.h>
-#if CONFIG(SOUTHBRIDGE_INTEL_I82801GX)
-#include <southbridge/intel/i82801gx/i82801gx.h> /* smbus_read_byte */
-#else
-#include <southbridge/intel/i82801jx/i82801jx.h> /* smbus_read_byte */
-#endif
 #include <spd.h>
 #include <string.h>
 #include <device/dram/ddr2.h>