[PATCH] ppc64: enforce medium thread priority in hypervisor calls

Calls into the hypervisor do not raise the thread priority.  Ensure we are
running at medium priority upon entry to the hypervisor.

Signed-off-by: Anton Blanchard <anton@samba.org>
Signed-off-by: Andrew Morton <akpm@osdl.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>