MIPS: bmips: Add support PCIe controller device nodes

For Broadcom STB PCIe HW. The 7425 and 7435 are MIPs-based SOCs.  Not much
difference between the two for the DT properties except that they have
slightly different PCIe interrupt assignments.

Signed-off-by: Jim Quinlan <jim2101024@gmail.com>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>