apex: support prebuilt_firmware for vendor apexes

prebuilt_firmware module is one of many prebuilt_etc-like modules. When
it is soc-specific, it is installed in /vendor/firmware. Similarly, when
prebuilt_firmware is embeded in a vendor apex, installing it in
<apex>/firmware instead of <apex>/etc.

Bug: 162701747
Test: lunch sunfish-userdebug
      m && device boots && vibrator works
Change-Id: I00d28cde42259aaf8221e3897df77efc42b0c1ca

apex/apex_test.go

@@ -248,7 +248,7 @@ func testApexContext(_ *testing.T, bp string, handlers ...testCustomizer) (*andr
 	ctx.RegisterModuleType("cc_test", cc.TestFactory)
 	ctx.RegisterModuleType("vndk_prebuilt_shared", cc.VndkPrebuiltSharedFactory)
 	ctx.RegisterModuleType("vndk_libraries_txt", cc.VndkLibrariesTxtFactory)
-	ctx.RegisterModuleType("prebuilt_etc", prebuilt_etc.PrebuiltEtcFactory)
+	prebuilt_etc.RegisterPrebuiltEtcBuildComponents(ctx)
 	ctx.RegisterModuleType("platform_compat_config", java.PlatformCompatConfigFactory)
 	ctx.RegisterModuleType("sh_binary", sh.ShBinaryFactory)
 	ctx.RegisterModuleType("filegroup", android.FileGroupFactory)
@@ -2272,6 +2272,32 @@ func TestVendorApex_use_vndk_as_stable(t *testing.T) {
 	ensureListContains(t, requireNativeLibs, ":vndk")
 }
 
+func TestVendorApex_withPrebuiltFirmware(t *testing.T) {
+	ctx, _ := testApex(t, `
+		apex {
+			name: "myapex",
+			key: "myapex.key",
+			prebuilts: ["myfirmware"],
+			vendor: true,
+		}
+		apex_key {
+			name: "myapex.key",
+			public_key: "testkey.avbpubkey",
+			private_key: "testkey.pem",
+		}
+		prebuilt_firmware {
+			name: "myfirmware",
+			src: "myfirmware.bin",
+			filename_from_src: true,
+			vendor: true,
+		}
+	`)
+
+	ensureExactContents(t, ctx, "myapex", "android_common_myapex_image", []string{
+		"firmware/myfirmware.bin",
+	})
+}
+
 func TestAndroidMk_UseVendorRequired(t *testing.T) {
 	ctx, config := testApex(t, `
 		apex {