lib/genalloc.c: use vzalloc_node() to allocate the bitmap

lib/genalloc.c: use vzalloc_node() to allocate the bitmap

[ Upstream commit 6862d2fc81859f88c1f3f660886427893f2b4f3f ]

Some devices may have big memory on chip, such as over 1G.  In some
cases, the nbytes maybe bigger then 4M which is the bounday of the
memory buddy system (4K default).

So use vzalloc_node() to allocate the bitmap.  Also use vfree to free
it.

Link: http://lkml.kernel.org/r/20181225015701.6289-1-sjhuang@iluvatar.ai
Signed-off-by: Huang Shijie <sjhuang@iluvatar.ai>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Alexey Skidanov <alexey.skidanov@intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>