bootimg supports v4 header

It's the latest version of android boot image header which supports
bootconfig. Bootconfig parameters are now passed via `bootconfig`
property.

Bug: 181936566
Test: m microdroid_boot

Change-Id: Iff8697434f7502fe56fca5bce5573e53f2f6ac60

filesystem/bootimg.go

@@ -62,6 +62,10 @@ type bootimgProperties struct {
 	// Optional kernel commandline
 	Cmdline *string
 
+	// File that contains bootconfig parameters. This can be set only when `vendor_boot` is true
+	// and `header_version` is greater than or equal to 4.
+	Bootconfig *string `android:"arch_variant,path"`
+
 	// When set to true, sign the image with avbtool. Default is false.
 	Use_avb *bool
 
@@ -189,6 +193,19 @@ func (b *bootimg) buildBootImage(ctx android.ModuleContext, vendor bool) android
 		return output
 	}
 
+	bootconfig := proptools.String(b.properties.Bootconfig)
+	if bootconfig != "" {
+		if !vendor {
+			ctx.PropertyErrorf("bootconfig", "requires vendor_boot: true")
+			return output
+		}
+		if verNum < 4 {
+			ctx.PropertyErrorf("bootconfig", "requires header_version: 4 or later")
+			return output
+		}
+		cmd.FlagWithInput("--vendor_bootconfig ", android.PathForModuleSrc(ctx, bootconfig))
+	}
+
 	flag := "--output "
 	if vendor {
 		flag = "--vendor_boot "