lockdep, rwsem: provide down_write_nest_lock()

down_write_nest_lock() provides a means to annotate locking
scenario
where an outer lock is guaranteed to serialize the order nested
locks
are being acquired.

This is analogoue to already existing
mutex_lock_nest_lock() and
spin_lock_nest_lock().

Change-Id:
Ib6124fd59cfc01c225cdb6fa46eec2b6d57f8c18
Signed-off-by: Jiri Kosina
<jkosina@suse.cz>
Cc: Rik van Riel <riel@redhat.com>
Cc: Ingo Molnar
<mingo@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Cc: Mel
Gorman <mel@csn.ul.ie>
Tested-by: Sedat Dilek
<sedat.dilek@gmail.com>
Signed-off-by: Andrew Morton
<akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds
<torvalds@linux-foundation.org>

idea is taken here -
https://github.com/jrior001/android_kernel_samsung_d2/commit/310562f1e3619115cba19db86b59387905967052