powerpc: introduce ePAPR embedded hypervisor hcall interface

ePAPR hypervisors provide operating system services via a "hypercall"
interface.  The following steps need to be performed to make an hcall:

1. Load r11 with the hcall number
2. Load specific other registers with parameters
3. Issue instrucion "sc 1"
4. The return code is in r3
5. Other returned parameters are in other registers.

To provide this service to the kernel, these steps are wrapped in inline
assembly functions.  Standard ePAPR hcalls are in epapr_hcalls.h, and
Freescale extensions are in fsl_hcalls.h.
Signed-off-by: Timur Tabi <timur@freescale.com>
Signed-off-by: Kumar Gala <galak@kernel.crashing.org>