acpi: Add support for writing a _PRW

A 'Power Resource for Wake' list the resources a device depends on for
wake. Add a function to generate this.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/acpi/acpigen.c b/lib/acpi/acpigen.c
index c609ef4..527de89 100644
--- a/lib/acpi/acpigen.c
+++ b/lib/acpi/acpigen.c
@@ -426,6 +426,16 @@
 	acpigen_write_resourcetemplate_footer(ctx);
 }
 
+void acpigen_write_prw(struct acpi_ctx *ctx, uint wake, uint level)
+{
+	/* Name (_PRW, Package () { wake, level } */
+	acpigen_write_name(ctx, "_PRW");
+	acpigen_write_package(ctx, 2);
+	acpigen_write_integer(ctx, wake);
+	acpigen_write_integer(ctx, level);
+	acpigen_pop_len(ctx);
+}
+
 /*
  * ToUUID(uuid)
  *