tracing/slab: Move kmalloc tracepoint out of inline code

The tracepoint for kmalloc is in the slab inlined code which causes
every instance of kmalloc to have the tracepoint.

This patch moves the tracepoint out of the inline code to the
slab C file, which removes a large number of inlined trace
points.

  objdump -dr vmlinux.slab| grep 'jmpq.*<trace_kmalloc' |wc -l
213
  objdump -dr vmlinux.slab.patched| grep 'jmpq.*<trace_kmalloc' |wc -l
1

This also has a nice impact on size.

   text	   data	    bss	    dec	    hex	filename
7023060	2121564	2482432	11627056	 b16a30	vmlinux.slab
6970579	2109772	2482432	11562783	 b06f1f	vmlinux.slab.patched

Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
Signed-off-by: Pekka Enberg <penberg@kernel.org>