ARM: entry: ensure that IRQs are enabled when calling syscall_trace_exit()

The audit code looks like it's been written to cope with being called
with IRQs enabled.  However, it's unclear whether IRQs should be
enabled or disabled when calling the syscall tracing infrastructure.

Right now, sometimes we call this with IRQs enabled, and other times
with IRQs disabled.  Opt for IRQs being enabled for consistency.

Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>