perf map: Remove ->groups from 'struct map'

With this 'struct map' uses a bit over 3 cachelines:

  $ pahole -C map ~/bin/perf
  <SNIP>
  	/* --- cacheline 2 boundary (128 bytes) --- */
  	u64                        (*unmap_ip)(struct map *, u64); /*   128     8 */
  	struct dso *               dso;                            /*   136     8 */
  	refcount_t                 refcnt;                         /*   144     4 */

  	/* size: 152, cachelines: 3, members: 18 */
  	/* sum members: 145, holes: 1, sum holes: 3 */
  	/* padding: 4 */
  	/* forced alignments: 2 */
  	/* last cacheline: 24 bytes */
  } __attribute__((__aligned__(8)));
  $

We probably can move map->map/unmap_ip() moved to 'struct map_groups',
that will shave more 16 bytes, getting this almost to two cachelines.

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Andi Kleen <ak@linux.intel.com>
Cc: Jiri Olsa <jolsa@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Link: https://lkml.kernel.org/n/tip-ymlv3nzpofv2fugnjnizkrwy@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>