src/ec,mainboard: Move weak smbios_system_sku() override inwards

Internalise smbios_system_sku() strong symbol inwards in the ec_skuid.c
implementation and simply wrap a call to:
google_chromeec_smbios_system_sku().

BUG=b:150735116
BRANCH=none
TEST=none

Change-Id: I05ebfc8126c0fb176ca52c307c658f50611ab6ab
Signed-off-by: Edward O'Callaghan <quasisec@google.com>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/39146
Reviewed-by: Karthik Ramasubramanian <kramasub@google.com>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

src/ec/google/chromeec/ec_skuid.c

@@ -11,6 +11,7 @@
 #include <ec/google/chromeec/ec.h>
 #include <console/console.h>
 #include <string.h>
+#include <smbios.h>
 
 #define SKU_UNKNOWN		0xFFFFFFFF
 
@@ -34,3 +35,8 @@ const char *google_chromeec_smbios_system_sku(void)
 	snprintf(sku_str, sizeof(sku_str), "sku%u", sku_id);
 	return sku_str;
 }
+
+const char *smbios_system_sku(void)
+{
+	return google_chromeec_smbios_system_sku();
+}