powerpc: Disable CPU_FTR_TM if TM is disabled by firmware

[ Upstream commit 9e819963b45f79e87f5a8c44960a66c0727c80e6 ]

Firmware is allowed to communicate to us via the "ibm,pa-features" property
that TM (Transactional Memory) support is disabled.

Currently this doesn't happen on any platform we're aware of, but we should
honor it anyway.

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.vnet.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Signed-off-by: Sasha Levin <sasha.levin@oracle.com>