powerpc: Register defines for various transactional memory registers

Defines for MSR bits and transactional memory related SPRs TFIAR, TEXASR and
TEXASRU.

Signed-off-by: Matt Evans <matt@ozlabs.org>
Signed-off-by: Michael Neuling <mikey@neuling.org>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>