Account for multiple BOARD_PLAT_PUBLIC[PRIVATE]_SEPOLICY_DIR dirs

After https://android-review.googlesource.com/688488
BOARD_PLAT_PUBLIC[PRIVATE]_SEPOLICY_DIR can now specify multiple
directories.

Bug: n/a
Test: build sepolicy
Change-Id: Ie2af81a4f9462cd05352db71fd1e515531d42334

build/soong/filegroup.go

@@ -122,8 +122,8 @@ func (fg *fileGroup) GenerateAndroidBuildActions(ctx android.ModuleContext) {
 	fg.systemVendorSrcs = fg.findSrcsInDir(ctx, filepath.Join(ctx.ModuleDir(), "vendor"))
 	fg.systemReqdMaskSrcs = fg.findSrcsInDir(ctx, filepath.Join(ctx.ModuleDir(), "reqd_mask"))
 
-	fg.systemExtPublicSrcs = fg.findSrcsInDir(ctx, ctx.DeviceConfig().PlatPublicSepolicyDir())
-	fg.systemExtPrivateSrcs = fg.findSrcsInDir(ctx, ctx.DeviceConfig().PlatPrivateSepolicyDir())
+	fg.systemExtPublicSrcs = fg.findSrcsInDirs(ctx, ctx.DeviceConfig().PlatPublicSepolicyDirs())
+	fg.systemExtPrivateSrcs = fg.findSrcsInDirs(ctx, ctx.DeviceConfig().PlatPrivateSepolicyDirs())
 
 	fg.vendorSrcs = fg.findSrcsInDirs(ctx, ctx.DeviceConfig().VendorSepolicyDirs())
 	fg.odmSrcs = fg.findSrcsInDirs(ctx, ctx.DeviceConfig().OdmSepolicyDirs())