[MLX4] return different MLX4 bus locations for several cards in multi-homed machine...

[MLX4] return different MLX4 bus locations for several cards in multi-homed machine. [mlnx: 4468]

One can see on multi-homed computers, that mlx4_bus creates all its children (mlx4_hca, IPoIB et al) with built-in location string "MLX4 Bus 0" which complicates differentiation between them.
This patch makes mlx4_bus to return a location string of the structure "MLX4 bus x, device y, function z", where x,y,z is HCA card's PCI bus location.

git-svn-id: svn://openib.tc.cornell.edu/gen1@2258 ad392aa1-c5ef-ae45-8dd8-e69d62a5ef86