ppc: BOOK3E: nothing should be done when MSR:PR is set

The server architecture (BOOK3S) specifies that any instruction that
sets MSR:PR will also set MSR:EE, IR and DR.
However there is no such behavior specification for the embedded
architecture (BOOK3E).

Signed-off-by: Vladimir Svoboda <ze.vlad@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Thomas Huth <thuth@redhat.com>