rtc: sun6i: add support for R329 RTC

Allwinner R329 has a RTC with a similar time storage with H616 but a
slightly different clock part.

As we have already handled the R329 RTC clocks in the CCU driver, add a
compatible string to RTC driver to allow probing of the RTC.

Signed-off-by: Icenowy Zheng <icenowy@aosc.io>
Signed-off-by: Samuel Holland <samuel@sholland.org>
Tested-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Reviewed-by: Jernej Skrabec <jernej.skrabec@gmail.com>
Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Link: https://lore.kernel.org/r/20220626042756.58961-1-samuel@sholland.org