soc/amd/picasso/southbridge: add missing soc/i2c.h include

soc/i2c.h gets included indirectly via chip.h and removing the chip.h
in 73716d0e92 broke the build. chip.h got
added back, but including soc/i2c.h directly fixes the underlying issue.

Change-Id: Ic84f7b6b4447b7c335a51dc604daf8924851e555
Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/41557
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Raul Rangel <rrangel@chromium.org>
Reviewed-by: Furquan Shaikh <furquan@google.com>

src/soc/amd/picasso/southbridge.c

@@ -17,6 +17,7 @@
 #include <amdblocks/acpi.h>
 #include <amdblocks/spi.h>
 #include <soc/cpu.h>
+#include <soc/i2c.h>
 #include <soc/southbridge.h>
 #include <soc/smi.h>
 #include <soc/amd_pci_int_defs.h>