Added int Nface as a template parameter in the
StaggeredDslashCuda class.
This class is defined in lib/dslash_quda.cu.
nFace is set to 3 by default.
The kernel body in dslash_core/staggered_dslash_def.h was updated
accordingly.
Also removed an argument from cuda(cpu)ColorSpinorField::unpackGhost.