rtc: sun6i: Disable the build as a module

Since we have to provide the clock very early on, the RTC driver cannot be
built as a module. Make sure that won't happen.

Cc: [e-mail]
Signed-off-by: Maxime Ripard <[e-mail]>
Signed-off-by: Alexandre Belloni <[e-mail]>

drivers/rtc/Kconfig

···
 	  based RTC on SUN4V systems.
 
 config RTC_DRV_SUN6I
-	tristate "Allwinner A31 RTC"
+	bool "Allwinner A31 RTC"
 	default MACH_SUN6I || MACH_SUN8I || COMPILE_TEST
 	depends on ARCH_SUNXI
 	help

drivers/rtc/rtc-sun6i.c

···
 		.of_match_table = sun6i_rtc_dt_ids,
 	},
 };
-
-module_platform_driver(sun6i_rtc_driver);
-
-MODULE_DESCRIPTION("sun6i RTC driver");
-MODULE_AUTHOR("Chen-Yu Tsai <[e-mail]>");
-MODULE_LICENSE("GPL");
+builtin_platform_driver(sun6i_rtc_driver);