arm64: audit: Add audit hook in syscall_trace_enter/exit()

This patch adds auditing functions on entry to or exit from
every system call invocation.

Acked-by: Richard Guy Briggs <rgb@redhat.com>
Acked-by Will Deacon <will.deacon@arm.com>
Signed-off-by: AKASHI Takahiro <takahiro.akashi@linaro.org>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

Conflicts:
	arch/arm64/kernel/ptrace.c

Change-Id: I7ebff5df4acbdab56c74e584dbc5fef5d8bfc9a8