memory: mtk-smi: Allow building as module

Add support for building the SMI driver as module. Switch MTK_SMI to
tristate, and add module_exit/module_license.

Signed-off-by: Yong Wu <yong.wu@mediatek.com>
Link: https://lore.kernel.org/r/20210126060055.11050-1-yong.wu@mediatek.com
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>

drivers/memory/Kconfig

@@ -173,7 +173,7 @@ config JZ4780_NEMC
 	  memory devices such as NAND and SRAM.
 
 config MTK_SMI
-	bool "Mediatek SoC Memory Controller driver" if COMPILE_TEST
+	tristate "MediaTek SoC Memory Controller driver" if COMPILE_TEST
 	depends on ARCH_MEDIATEK || COMPILE_TEST
 	help
 	  This driver is for the Memory Controller module in MediaTek SoCs,

drivers/memory/mtk-smi.c

@@ -597,3 +597,12 @@ static int __init mtk_smi_init(void)
 	return platform_register_drivers(smidrivers, ARRAY_SIZE(smidrivers));
 }
 module_init(mtk_smi_init);
+
+static void __exit mtk_smi_exit(void)
+{
+	platform_unregister_drivers(smidrivers, ARRAY_SIZE(smidrivers));
+}
+module_exit(mtk_smi_exit);
+
+MODULE_DESCRIPTION("MediaTek SMI driver");
+MODULE_LICENSE("GPL v2");

include/soc/mediatek/smi.h

@@ -9,7 +9,7 @@
 #include <linux/bitops.h>
 #include <linux/device.h>
 
-#ifdef CONFIG_MTK_SMI
+#if IS_ENABLED(CONFIG_MTK_SMI)
 
 #define MTK_LARB_NR_MAX		16