ARM: dts: imx7d-sdb: Set VLDO4 outpt to 2.8V for MIPI CSI/DSI

According to mx7sabresd schematics the MIPI CSI/DSI voltage rails
should be 2.8V but the voltage provided is a maximum of 3.3V and
minimum of 1.8V. Providing such a higher voltage might damage the
peripherals and violates the schematic settings.

Signed-off-by: Gautam Bhat <mindentropy@gmail.com>
Reviewed-by: Fabio Estevam <fabio.estevam@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>