This patch implements the perf registers sampling and validation API
for the riscv arch. The valid registers and their register ID are
defined in perf_regs.h. Perf tool can backtrace in userspace with
unwind library and the registers/user stack dump support.
Signed-off-by: Mao Han <han_mao@c-sky.com> Cc: Paul Walmsley <paul.walmsley@sifive.com> Cc: Greentime Hu <green.hu@gmail.com> Cc: Palmer Dabbelt <palmer@sifive.com> Cc: linux-riscv <linux-riscv@lists.infradead.org> Cc: Christoph Hellwig <hch@lst.de> Cc: Guo Ren <guoren@kernel.org> Tested-by: Greentime Hu <greentime.hu@sifive.com>
[paul.walmsley@sifive.com: minor patch description fix] Signed-off-by: Paul Walmsley <paul.walmsley@sifive.com>