arm64: ptrace: add support for syscall emulation

Add PTRACE_SYSEMU and PTRACE_SYSEMU_SINGLESTEP support on arm64.
We don't need any special handling for PTRACE_SYSEMU_SINGLESTEP.

It's quite difficult to generalize handling PTRACE_SYSEMU cross
architectures and avoid calls to tracehook_report_syscall_entry twice.
Different architecture have different mechanism to indicate NO_SYSCALL
and trying to generalise adds more code for no gain.

Cc: Will Deacon <will.deacon@arm.com>
Signed-off-by: Sudeep Holla <sudeep.holla@arm.com>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>