perf tools: Use __map__is_kernel() when synthesizing kernel module mmap records

perf tools: Use __map__is_kernel() when synthesizing kernel module mmap records

Equivalent and removes one more case of using dso->kernel.

  # perf record -a usleep 1
  [ perf record: Woken up 1 times to write data ]
  [ perf record: Captured and wrote 0.768 MB perf.data (30 samples) ]

Before:

  [root@zoo ~]# perf script --show-task --show-mmap | head -3
   swapper 0 [0] 0.0: PERF_RECORD_MMAP -1/0: [0xffffffff81000000(0x1f000000) @ 0xffffffff81000000]: x [kernel.kallsyms]_text
   swapper 0 [0] 0.0: PERF_RECORD_MMAP -1/0: [0xffffffffa0000000(0xa000) @ 0]: x /lib/modules/4.3.0-rc1+/kernel/drivers/acpi/video.ko
   swapper 0 [0] 0.0: PERF_RECORD_MMAP -1/0: [0xffffffffa000a000(0x5000) @ 0]: x /lib/modules/4.3.0-rc1+/kernel/drivers/i2c/algos/i2c-algo-bit.ko
  #

  # perf script --show-task --show-mmap | head -3
   swapper 0 [0] 0.0: PERF_RECORD_MMAP -1/0: [0xffffffff81000000(0x1f000000) @ 0xffffffff81000000]: x [kernel.kallsyms]_text
   swapper 0 [0] 0.0: PERF_RECORD_MMAP -1/0: [0xffffffffa0000000(0xa000) @ 0]: x /lib/modules/4.3.0-rc1+/kernel/drivers/acpi/video.ko
   swapper 0 [0] 0.0: PERF_RECORD_MMAP -1/0: [0xffffffffa000a000(0x5000) @ 0]: x /lib/modules/4.3.0-rc1+/kernel/drivers/i2c/algos/i2c-algo-bit.ko
  #

Cc: Adrian Hunter <adrian.hunter@intel.com>
Cc: Borislav Petkov <bp@suse.de>
Cc: David Ahern <dsahern@gmail.com>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Stephane Eranian <eranian@google.com>
Cc: Wang Nan <wangnan0@huawei.com>
Link: http://lkml.kernel.org/n/tip-b65xe578dwq22mzmmj5y94wr@git.kernel.org
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>