Map perf APIs (perf_reg_name/get_arch_regstr/unwind__arch_reg_id) with
MIPS specific registers.

[ayan@wavecomp.com: repick this patch for unwinding userstack backtrace
by perf and libunwind on MIPS based CPU.]

[yangtiezhu@loongson.cn: Add sample_reg_masks[] to fix build error,
silence some checkpatch errors and warnings, and also separate the
original patches into two parts (MIPS kernel and perf tools) to merge
easily.]

The original patches:

https://lore.kernel.org/patchwork/patch/1126521/
https://lore.kernel.org/patchwork/patch/1126520/

Committer notes:

Do it as __perf_reg_name() to cope with:

  06701297 ("perf tools: Fix arm64 build error with gcc-11")
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Archer Yan <ayan@wavecomp.com>
Cc: David Daney <david.daney@cavium.com>
Cc: Jianlin Lv <Jianlin.Lv@arm.com>
Cc: Jiri Olsa <jolsa@redhat.com>
Cc: Juxin Gao <gaojuxin@loongson.cn>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Namhyung Kim <namhyung@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Ralf Baechle <ralf@linux-mips.org>
Cc: Xuefeng Li <lixuefeng@loongson.cn>
Cc: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Cc: linux-mips@vger.kernel.org
Link: http://lore.kernel.org/lkml/1612409724-3516-3-git-send-email-yangtiezhu@loongson.cnSigned-off-by: Archer Yan <ayan@wavecomp.com>
Signed-off-by: David Daney <david.daney@cavium.com>
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
Signed-off-by: Arnaldo Carvalho de Melo <acme@redhat.com>