Add initial port for Broadcom Stingray SOC.

Stingray SOC has ARMv8 based 4 clusters of dual core Cortex-A72 processors,
arm CCN interconnect, GICv3 based arm GIC500, ns16550 UART.
Initial support may have only QSPI boot mode.

ROM (equivalent to BL1) will have the capability to load image from FIP and jump to BL2.
Hence the initial port to have BL2, BL31.