[POWERPC] Add SPRN for Embedded registers specified in PowerISA 2.04

* Added SPRN for new architectural features added for embedded:
	- Alternate Time Base (ATB, ATBL, ATBU)
	- Doorbell Interrupts (IVOR36, IVOR37)
	- SPRG8/9
	- External Proxy (EPR)
	- External PID load/store (EPLC, EPSC)

* Added BUCSR for Freescale Embedded Processors
* Moved around MAS7 so its in numeric order

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