powerpc/booke: Add support for new e500mc core

The new e500mc core from Freescale is based on the e500v2 but with the
following changes:

* Supports only the Enhanced Debug Architecture (DSRR0/1, etc)
* Floating Point
* No SPE
* Supports lwsync
* Doorbell Exceptions
* Hypervisor
* Cache line size is now 64-bytes (e500v1/v2 have a 32-byte cache line)

Signed-off-by: Kumar Gala <galak@kernel.crashing.org>