sb/intel/common: Add early SPI code

All Intel southbridges with SPI perform this write. Put it inside a
function in common code. Use a different name to avoid a name clash.

As it is only one statement, make it inline so that it can be defined
on the header itself. It is only called once per southbridge anyway.

Change-Id: I3c284d6cffd22949d50b4c4f9846ceaef38d7cda
Signed-off-by: Angel Pons <th3fanbus@gmail.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/42660
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Rudolph <siro@das-labor.org>

src/southbridge/intel/common/early_spi.h

@@ -0,0 +1,13 @@
+/* SPDX-License-Identifier: GPL-2.0-only */
+
+#ifndef SOUTHBRIDGE_INTEL_COMMON_EARLY_SPI_H
+#define SOUTHBRIDGE_INTEL_COMMON_EARLY_SPI_H
+
+#include <device/pci_ops.h>
+
+static inline void enable_spi_prefetching_and_caching(void)
+{
+	pci_update_config8(PCI_DEV(0, 0x1f, 0), 0xdc, ~(3 << 2), 2 << 2);
+}
+
+#endif