Soong support for rollback index.

avbtool already supports --rollback_index. Allow soong support as well
to enable images to include it in their targets.

Test: Builds
Test: avbtool info_image on a target built using rule `avb_add_hash_footer`
Bug: 296830692
Change-Id: Id32f30d026b01172c5dadc0698938acb2c2c8e35

filesystem/avb_add_hash_footer.go

@@ -68,6 +68,9 @@ type avbAddHashFooterProperties struct {
 	// List of properties to add to the footer
 	Props []avbProp
 
+	// The index used to prevent rollback of the image on device.
+	Rollback_index *int64
+
 	// Include descriptors from images
 	Include_descriptors_from_images []string `android:"path,arch_variant"`
 }
@@ -128,6 +131,14 @@ func (a *avbAddHashFooter) GenerateAndroidBuildActions(ctx android.ModuleContext
 		addAvbProp(ctx, cmd, prop)
 	}
 
+	if a.properties.Rollback_index != nil {
+		rollbackIndex := proptools.Int(a.properties.Rollback_index)
+		if rollbackIndex < 0 {
+			ctx.PropertyErrorf("rollback_index", "Rollback index must be non-negative")
+		}
+		cmd.Flag(fmt.Sprintf(" --rollback_index %x", rollbackIndex))
+	}
+
 	cmd.FlagWithOutput("--image ", a.output)
 
 	builder.Build("avbAddHashFooter", fmt.Sprintf("avbAddHashFooter %s", ctx.ModuleName()))