gru: dynamic allocation of kernel contexts

Change the interface to gru_alloc_gts() so that it can be used to allocate
GRU contexts for kernel threads.  Kernel threads do not have vdata
structures for the GRU contexts.  The GRU resource count are now passed
explicitly instead of inside the vdata structure.

Signed-off-by: Jack Steiner <steiner@sgi.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>