mb/amd/bilby,mandolin: add missing string.h include

string.h defines the memset function.

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I242a0382e7020681b6c3a25f75a2a91cbccbe815
Reviewed-on: https://review.coreboot.org/c/coreboot/+/68844
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Fred Reitberger <reitbergerfred@gmail.com>

src/mainboard/amd/bilby/mainboard.c

@@ -9,6 +9,7 @@
 #include <soc/southbridge.h>
 #include <soc/pci_devs.h>
 #include <soc/platform_descriptors.h>
+#include <string.h>
 #include <types.h>
 #include <commonlib/helpers.h>
 #include <soc/amd/picasso/chip.h>

src/mainboard/amd/mandolin/mainboard.c

@@ -7,6 +7,7 @@
 #include <soc/cpu.h>
 #include <soc/southbridge.h>
 #include <soc/pci_devs.h>
+#include <string.h>
 #include <types.h>
 #include <commonlib/helpers.h>
 #include <soc/amd/picasso/chip.h>