arm64: dts: lx2160a-cex7: add support for ltc3882 regulator

Add support for the LTC3882 regulator so that the hardware monitoring
can be used with this device.  This regulator provides the 0.78V
supply for the LX2160A.

Signed-off-by: Russell King <rmk+kernel@armlinux.org.uk>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>