workqueue: Basic memory allocation profiling support

Hook alloc_workqueue and alloc_workqueue_attrs() so that they're
accounted to the callsite. Since we're doing allocations on behalf of
another subsystem, this helps when using memory allocation profiling to
check for leaks.

Cc: Tejun Heo <tj@kernel.org>
Cc: Lai Jiangshan <jiangshanlai@gmail.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Tejun Heo <tj@kernel.org>