perf build: Remove PERF_HAVE_DWARF_REGS

PERF_HAVE_DWARF_REGS was true when an architecture had a dwarf-regs.c
file. There are no more architecture dwarf-regs.c files, selection is
done using constants from the ELF file rather than conditional
compilation. When removing PERF_HAVE_DWARF_REGS was the only variable
in the Makefile, remove the Makefile.

Add missing SPDX for RISC-V Makefile.

Reviewed-by: Masami Hiramatsu (Google) <mhiramat@kernel.org>
Signed-off-by: Ian Rogers <irogers@google.com>
Cc: Anup Patel <anup@brainfault.org>
Cc: Yang Jihong <yangjihong@bytedance.com>
Cc: Palmer Dabbelt <palmer@dabbelt.com>
Cc: David S. Miller <davem@davemloft.net>
Cc: Albert Ou <aou@eecs.berkeley.edu>
Cc: Shenlin Liang <liangshenlin@eswincomputing.com>
Cc: Nick Terrell <terrelln@fb.com>
Cc: Guilherme Amadio <amadio@gentoo.org>
Cc: Steinar H. Gunderson <sesse@google.com>
Cc: Changbin Du <changbin.du@huawei.com>
Cc: Alexander Lobakin <aleksander.lobakin@intel.com>
Cc: Przemek Kitszel <przemyslaw.kitszel@intel.com>
Cc: Huacai Chen <chenhuacai@kernel.org>
Cc: Guo Ren <guoren@kernel.org>
Cc: Masahiro Yamada <masahiroy@kernel.org>
Cc: Will Deacon <will@kernel.org>
Cc: James Clark <james.clark@linaro.org>
Cc: Mike Leach <mike.leach@linaro.org>
Cc: Chen Pei <cp0613@linux.alibaba.com>
Cc: Leo Yan <leo.yan@linux.dev>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: Aditya Gupta <adityag@linux.ibm.com>
Cc: Kajol Jain <kjain@linux.ibm.com>
Cc: Athira Rajeev <atrajeev@linux.vnet.ibm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: linux-riscv@lists.infradead.org
Cc: Bibo Mao <maobibo@loongson.cn>
Cc: John Garry <john.g.garry@oracle.com>
Cc: Atish Patra <atishp@rivosinc.com>
Cc: Dima Kogan <dima@secretsauce.net>
Cc: Paul Walmsley <paul.walmsley@sifive.com>
Cc: Dr. David Alan Gilbert <linux@treblig.org>
Cc: linux-csky@vger.kernel.org
Link: https://lore.kernel.org/r/20241108234606.429459-21-irogers@google.com


Signed-off-by: Namhyung Kim <namhyung@kernel.org>