C6x: fix sys_set_tls() for vfork() case

Normally thread.tls field is updated during resume() but it needs
to be set earlier too in case of a vfork() occuring before we
did a first context switch. Child must inherit from parent TLS.

Signed-off-by: Aurelien Jacquiot <a-jacquiot@ti.com>
Merge branch 'master' of git://linux-c6x.org/git/linux-c6x into ac-dsp