rtase: Add a Makefile in the rtase folder

Add a Makefile in the rtase folder to build rtase driver.
Signed-off-by: Justin Lai <justinlai0215@realtek.com>
Link: https://patch.msgid.link/20240904032114.247117-12-justinlai0215@realtek.comSigned-off-by: Jakub Kicinski <kuba@kernel.org>

drivers/net/ethernet/realtek/rtase/Makefile

+# SPDX-License-Identifier: GPL-2.0 OR BSD-3-Clause
+# Copyright(c) 2024 Realtek Semiconductor Corp. All rights reserved.
+
+#
+# Makefile for the Realtek PCIe driver
+#
+
+obj-$(CONFIG_RTASE) += rtase.o
+
+rtase-objs := rtase_main.o