arm64: ftrace: Fix to enable syscall events on arm64

Since commit 4378a7d4 ("arm64: implement syscall wrappers")
introduced "__arm64_" prefix to all syscall wrapper symbols in
sys_call_table, syscall tracer can not find corresponding
metadata from syscall name. In the result, we have no syscall
ftrace events on arm64 kernel, and some bpf testcases are failed
on arm64.

To fix this issue, this introduces custom
arch_syscall_match_sym_name() which skips first 8 bytes when
comparing the syscall and symbol names.

Fixes: 4378a7d4

 ("arm64: implement syscall wrappers")
Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>
Acked-by: Will Deacon <will.deacon@arm.com>
Tested-by: Naresh Kamboju <naresh.kamboju@linaro.org>
Cc: stable@vger.kernel.org
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>