sunxi: add rtc-sun6i driver package

sunxi: add rtc-sun6i driver package

AP6212 wifi need wifi_pwrseq, but from OrangePi Lite 2 dts :

wifi_pwrseq: wifi_pwrseq {
	compatible = "mmc-pwrseq-simple";
	clocks = <&rtc 1>;
	clock-names = "ext_clock";
	reset-gpios = <&r_pio 1 3 GPIO_ACTIVE_LOW>; /* PM3 */
	post-power-on-delay-ms = <200>;
};

this pwrseq need rtc clock, or kernel won't find this device.
but now rtc-sunxi.c only support A10/A20.
Orangepi Lite 2 use H6 ,from rtc-sun6i.c show compatible is
	{ .compatible = "allwinner,sun6i-a31-rtc" },
	{ .compatible = "allwinner,sun8i-a23-rtc" },
	{ .compatible = "allwinner,sun8i-h3-rtc" },
	{ .compatible = "allwinner,sun8i-r40-rtc" },
	{ .compatible = "allwinner,sun8i-v3-rtc" },
	{ .compatible = "allwinner,sun50i-h5-rtc" },
	{ .compatible = "allwinner,sun50i-h6-rtc" },
So it need this to let kernel find this mmc wifi device.

As suggested by hauke, let it build as package.

Signed-off-by: Zhao Yu <574249312@qq.com>