acpi: Add function to simplify If (CondRefOf (..)) sequences

The new function is called acpigen_write_if_cond_refof(), and it must
be paired with a following acpigen_write_if_end() call.

Change-Id: I6e192a569f550ecb77ad264275d52f219eacaca1
Signed-off-by: Tim Wawrzynczak <twawrzynczak@chromium.org>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/56003
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Patrick Georgi <pgeorgi@google.com>
diff --git a/src/acpi/acpigen.c b/src/acpi/acpigen.c
index 9818dc2..8320b6c 100644
--- a/src/acpi/acpigen.c
+++ b/src/acpi/acpigen.c
@@ -1501,6 +1501,21 @@
 	acpigen_write_integer(val);
 }
 
+/*
+ * Generates ACPI code to check at runtime if an object named `namestring`
+ * exists, and leaves the If scope open to continue execute code when this
+ * is true. NOTE: Requires matching acpigen_write_if_end().
+ *
+ * If (CondRefOf (NAME))
+ */
+void acpigen_write_if_cond_ref_of(const char *namestring)
+{
+	acpigen_write_if();
+	acpigen_emit_ext_op(COND_REFOF_OP);
+	acpigen_emit_namestring(namestring);
+	acpigen_emit_byte(ZERO_OP); /* ignore COND_REFOF_OP destination */
+}
+
 /* Closes previously opened if statement and generates ACPI code for else statement. */
 void acpigen_write_else(void)
 {