xfs: replace KM_LARGE with explicit vmalloc use

We use the KM_LARGE flag to make kmem_alloc and friends use vmalloc
if necessary.  As we only need this for a few boot/mount time
allocations just switch to explicit vmalloc calls there.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Alex Elder <aelder@sgi.com>