layerscape: add 64b/32b target for ls1046ardb device

Add support for NXP layerscape ls1046ardb 64b/32b Dev board.

LS1046ARDB Specification:
-------------------------
Memory subsystem:
* 8GByte DDR4 SDRAM (64bit bus)
* 512 Mbyte NAND flash
* Two 64 Mbyte high-speed SPI flash
* SD connector to interface with the SD memory card
* On-board 4G eMMC
Ethernet:
* Two XFI 10G ports
* Two SGMII ports
* Two RGMII ports
PCIe:
* PCIe1 (SerDes2 Lane0) to miniPCIe slot
* PCIe2 (SerDes2 Lane1) to x2 PCIe slot
* PCIe3 (SerDes2 Lane2) to x4 PCIe slot

* USB 3.0: one super speed USB 3.0 type A port, one Micro-AB port
* UART: supports two UARTs up to 115200 bps for console

Signed-off-by: Yutang Jiang <yutang.jiang@nxp.com>