layerscape: add LS1021AIOT board support

layerscape: add LS1021AIOT board support

The LS1021A-IoT gateway reference design based on the
QorIQ LS1021A processor is a purpose-built, small
footprint hardware platform with a wide array of
high-speed connectivity and low-speed serial interfaces
to support secure delivery of IoT services for home,
business or other commercial location.

- Combines standards-based, open source software with a
  feature-rich IoT gateway design to establish a common,
  open framework for secured IoT service delivery and
  management.

- Provides a wide assortment of high-speed and serial-based
  connectivity in a compact, highly secure design.

- High efficiency through the use of the Arm-based QorIQ
  LS1021A embedded processor.

Signed-off-by: Yangbo Lu <yangbo.lu@nxp.com>
Signed-off-by: Biwen Li <biwen.li@nxp.com>