arm64: dts: zii-ultra: Fix regulator-vsd-3v3's vin-supply

Regulator-vsd-3v3 is supplied via GEN_3V3 rail which is an output of
an "always on" load switch supplied by 3V3_MAIN. GEN_3V3 is also used
as vin-supply by a number of peripherals, so adding it also allows us
to follow the schematic more closely.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Cc: Fabio Estevam <festevam@gmail.com>
Cc: Chris Healy <cphealy@gmail.com>
Cc: Lucas Stach <l.stach@pengutronix.de>
Cc: Shawn Guo <shawnguo@kernel.org>
Cc: linux-arm-kernel@lists.infradead.org,
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Shawn Guo <shawnguo@kernel.org>