Add scripts/coccinelle/alloc/kzalloc-simple.cocci

This semantic patch replaces a pair of calls to kmalloc and memset
by a single call to kzalloc.

It only looks for simple cases to avoid false positives.

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