powerpc/spufs: fix npc setting for NOSCHED contexts

Currently, spu_run ignores the npc argument for contexts created with
SPU_CREATE_NOSCHED. While this is correct for isolated contexts,
there's no need to enforce the npc restriction on non-isolated NOSCHED
contexts.

This means that NOSCHED contexts can only ever run with an entry point
of 0x0.

This change to spu_run_init allows setting of the npc (and, while we're
at it, the privcntl) for non-isolated NOSCHED contexts. This allows
us to run NOSCHED contexts from any entry point.

Signed-off-by: Jeremy Kerr <jk@ozlabs.org>