ARM: brcmstb: Add default gpio number

Out of the brcmstb SoCs that I know, BCM3390 has the largest numbers
of GPIOs, with its
- 320 "peripheral" GPIOs
- 5*32 = 160 UPG GPIOs (counting unused lines, which do get counted)
- 2*32 = 64 UPG AON GPIOs (counting unused lines)
Total: 544

I suspect that the upper limit will only need to be higher in the
future, so set it to 1024.

Signed-off-by: Gregory Fong <gregory.0xf0@gmail.com>
Signed-off-by: Florian Fainelli <f.fainelli@gmail.com>