powerpc: Move the single step enable code to a generic path

powerpc: Move the single step enable code to a generic path

This patch moves the single step enable code used by kprobe to a generic
routine header so that, it can be re-used by other code, in this case,
uprobes. No functional changes.

Signed-off-by: Suzuki K. Poulose <[email protected]>
Cc:	Ananth N Mavinakaynahalli <[email protected]>
Cc:	Kumar Gala <[email protected]>
Cc:	[email protected]
Acked-by: Ananth N Mavinakayanahalli <[email protected]>
Signed-off-by: Benjamin Herrenschmidt <[email protected]>