mfd: Add module build support for RZ/G2L MTU3a

Modified Kconfig to enable module build support for RZ/G2L MTU3a driver.
While at it, added module.h header file.
Signed-off-by: Biju Das <biju.das.jz@bp.renesas.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/20230711092841.119161-1-biju.das.jz@bp.renesas.comSigned-off-by: Lee Jones <lee@kernel.org>

drivers/mfd/Kconfig

@@ -1371,7 +1371,7 @@ config MFD_SC27XX_PMIC
 	  and it also adds the irq_chip parts for handling the PMIC chip events.
 
 config RZ_MTU3
-	bool "Renesas RZ/G2L MTU3a core driver"
+	tristate "Renesas RZ/G2L MTU3a core driver"
 	depends on (ARCH_RZG2L && OF) || COMPILE_TEST
 	help
 	  Select this option to enable Renesas RZ/G2L MTU3a core driver for

drivers/mfd/rz-mtu3.c

@@ -11,6 +11,7 @@
 #include <linux/irq.h>
 #include <linux/mfd/core.h>
 #include <linux/mfd/rz-mtu3.h>
+#include <linux/module.h>
 #include <linux/of_platform.h>
 #include <linux/reset.h>
 #include <linux/spinlock.h>