rtc: jz4740: Rename vendor-specific DT properties

These properties are never set anywhere within any of the upstream
devicetree files, so I assume I'm not breaking the ABI with this change.

Rename vendor-specific DT properties to have the 'ingenic,' prefix,
which they should have had from the start.

Signed-off-by: Paul Cercueil <paul@crapouillou.net>
Link: https://lore.kernel.org/r/20200311182318.22154-2-paul@crapouillou.net


Signed-off-by: Alexandre Belloni <alexandre.belloni@bootlin.com>