Update the default core frequency to 1800MHZ for best performance under
SD boot and eMMC boot.

Signed-off-by: Gong Qianyu <Qianyu.Gong@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>

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

SATA:
 * SerDes2 Lane3 to SATA port

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: Mingkai Hu <mingkai.hu@nxp.com>
Signed-off-by: Shaohui Xie <Shaohui.Xie@nxp.com>
Signed-off-by: Gong Qianyu <Qianyu.Gong@nxp.com>
Reviewed-by: York Sun <york.sun@nxp.com>