powerpc/e6500: add TMCFG0 register definition

The register is not currently used in the base kernel
but will be in a forthcoming kvm patch.

Signed-off-by: Laurentiu Tudor <Laurentiu.Tudor@freescale.com>
Acked-by: Scott Wood <scottwood@freescale.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>