soc/amd/common/block/spi: Include mmio.h in fch_spi_ctrl.c

fch_spi_ctrl.c uses read*()/write*() functions which are declared in
arch/mmio.h. This change includes the file arch/mmio.h in
fch_spi_ctrl.c.

Signed-off-by: Furquan Shaikh <furquan@google.com>
Change-Id: I6540004512af1f59f5fb300a3a4818b87ad94bfa
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41271
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>

src/soc/amd/common/block/spi/fch_spi_ctrl.c

@@ -1,5 +1,6 @@
 /* SPDX-License-Identifier: GPL-2.0-only */
 
+#include <arch/mmio.h>
 #include <console/console.h>
 #include <spi_flash.h>
 #include <soc/pci_devs.h>