ARM: Add support for Broadcom BCM23550 SoC

BCM23550 is a quad-A7 SoC used on the Broadcom "Sparrow" board.
It shares many IP blocks with other Broadcom Kona chips.

Signed-off-by: Chris Brand <chris.brand@broadcom.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>