KVM: PPC: Book3S HV: Add userspace interfaces for POWER9 MMU

This adds two capabilities and two ioctls to allow userspace to
find out about and configure the POWER9 MMU in a guest.  The two
capabilities tell userspace whether KVM can support a guest using
the radix MMU, or using the hashed page table (HPT) MMU with a
process table and segment tables.  (Note that the MMUs in the
POWER9 processor cores do not use the process and segment tables
when in HPT mode, but the nest MMU does).

The KVM_PPC_CONFIGURE_V3_MMU ioctl allows userspace to specify
whether a guest will use the radix MMU or the HPT MMU, and to
specify the size and location (in guest space) of the process
table.

The KVM_PPC_GET_RMMU_INFO ioctl gives userspace information about
the radix MMU.  It returns a list of supported radix tree geometries
(base page size and number of bits indexed at each level of the
radix tree) and the encoding used to specify the various page
sizes for the TLB invalidate entry instruction.

Initially, both capabilities return 0 and the ioctls return -EINVAL,
until the necessary infrastructure for them to operate correctly
is added.

Signed-off-by: Paul Mackerras <paulus@ozlabs.org>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>