perf kmem: Consistently use PRIu64 for printing u64 values

Building the perf tool for 32-bit ARM results in the following build
error due to a combination of an incorrect conversion specifier and
compiling with -Werror:

  builtin-kmem.c: In function ‘print_page_summary’:
  builtin-kmem.c:644:9: error: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 3 has type ‘u64’ [-Werror=format=]
           nr_alloc_freed, (total_alloc_freed_bytes) / 1024);
           ^
  builtin-kmem.c:647:9: error: format ‘%lu’ expects argument of type ‘long unsigned int’, but argument 3 has type ‘u64’ [-Werror=format=]
           (total_page_alloc_bytes - total_alloc_freed_bytes) / 1024);
           ^
  cc1: all warnings being treated as errors

This patch fixes the problem by consistently using PRIu64 for printing
out u64 values.

Signed-off-by: Will Deacon <will.deacon@arm.com>
Cc: David Ahern <dsahern@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Joonsoo Kim <js1304@gmail.com>
Cc: Minchan Kim <minchan@kernel.org>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <a.p.zijlstra@chello.nl>
Link: http://lkml.kernel.org/r/1429796437-1790-1-git-send-email-will.deacon@arm.com
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>