arm64: dts: Add dts files for Hisilicon Hi3660 SoC

Add initial dtsi file to support Hisilicon Hi3660 SoC with
support of Octal core CPUs in two clusters(4 * A53 & 4 * A73).

Also add dts file to support HiKey960 development board which
based on Hi3660 SoC.
The output console is earlycon "earlycon=pl011,0xfdf05000".
And the con_init uart5 with a fixed clock, which already
configured at bootloader.

When clock is available, the uart5 will be modified.

Tested on HiKey960 Board.

Signed-off-by: Chen Feng <puck.chen@hisilicon.com>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Wei Xu <xuwei5@hisilicon.com>