ARM: dts: Add big-endian in nor node for ls1021a

NOR and IFC controller connectivity is big-endian.
So add big-endian field in nor device tree node allowing
IFC controller to read/write data from/to the flash correctly.

Signed-off-by: Prabhakar Kushwaha <prabhakar.kushwaha@nxp.com>
Acked-by: Li Yang <leoyang.li@nxp.com>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>