vendorcode/google: support multiple SAR filenames

Using a fixed filename only allows for one SAR configuration to be
checked into CBFS. However, we have devices with shared firmware that
would desire separate SAR configurations. This change allows boards to
define a function to select one of multiple files stored in CBFS to be
used.

BUG=b:120958726
BRANCH=octopus
TEST=build

Signed-off-by: Justin TerAvest <teravest@chromium.org>

Change-Id: Ib852aaaff39f1e9149fa43bf8dc25b2400737ea5
Reviewed-on: https://review.coreboot.org/c/30222
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Aaron Durbin <adurbin@chromium.org>

src/include/sar.h

@@ -54,4 +54,6 @@ struct wifi_sar_limits {
  */
 int get_wifi_sar_limits(struct wifi_sar_limits *sar_limits);
 
+const char *get_wifi_sar_cbfs_filename(void);
+
 #endif /* _SAR_H_ */