Coccinelle: Add locks/call_kern.cocci

Find functions that refer to GFP_KERNEL but are called with locks held.
The proposed change of converting the GFP_KERNEL is not necessarily the
correct one.  It may be desired to unlock the lock, or to not call the
function under the lock in the first place.

Signed-off-by: Nicolas Palix <npalix@diku.dk>
Signed-off-by: Julia Lawall <julia@diku.dk>
Signed-off-by: Michal Marek <mmarek@suse.cz>