powerpc: Update cpu_user_features2 in scan_features()

scan_features() updates cpu_user_features but not cpu_user_features2.

Amongst other things, cpu_user_features2 contains the user TM feature
bits which we must keep in sync with the kernel TM feature bit.

Signed-off-by: Anton Blanchard <anton@samba.org>
Cc: stable@vger.kernel.org
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>