powerpc: Set DSCR bit in FSCR setup

We support DSCR (Data Stream Control Register) so we should make sure we set it
in the FSCR (Facility Status & Control Register) incase some firmwares don't
set it.  If we don't set this, we'll take a facility unavailable exception when
using the DSCR.

Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>