arm64/bpf: correct broken uapi for BPF_PROG_TYPE_PERF_EVENT program type

Correct the broken uapi for the BPF_PROG_TYPE_PERF_EVENT program type
by exporting the user_pt_regs structure instead of the pt_regs structure
that is in-kernel only.

Signed-off-by: Hendrik Brueckner <brueckner@linux.vnet.ibm.com>
Reviewed-by: Thomas Richter <tmricht@linux.vnet.ibm.com>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Cc: Will Deacon <will.deacon@arm.com>
Cc: Mark Rutland <mark.rutland@arm.com>
Cc: Arnaldo Carvalho de Melo <acme@kernel.org>
Signed-off-by: Daniel Borkmann <daniel@iogearbox.net>