KVM: PPC: Book3S: Get/set guest SPRs using the GET/SET_ONE_REG interface

This enables userspace to get and set various SPRs (special-purpose
registers) using the KVM_[GS]ET_ONE_REG ioctls.  With this, userspace
can get and set all the SPRs that are part of the guest state, either
through the KVM_[GS]ET_REGS ioctls, the KVM_[GS]ET_SREGS ioctls, or
the KVM_[GS]ET_ONE_REG ioctls.

The SPRs that are added here are:

- DABR:  Data address breakpoint register
- DSCR:  Data stream control register
- PURR:  Processor utilization of resources register
- SPURR: Scaled PURR
- DAR:   Data address register
- DSISR: Data storage interrupt status register
- AMR:   Authority mask register
- UAMOR: User authority mask override register
- MMCR0, MMCR1, MMCRA: Performance monitor unit control registers
- PMC1..PMC8: Performance monitor unit counter registers

In order to reduce code duplication between PR and HV KVM code, this
moves the kvm_vcpu_ioctl_[gs]et_one_reg functions into book3s.c and
centralizes the copying between user and kernel space there.  The
registers that are handled differently between PR and HV, and those
that exist only in one flavor, are handled in kvmppc_[gs]et_one_reg()
functions that are specific to each flavor.

Signed-off-by: Paul Mackerras <paulus@samba.org>
[agraf: minimal style fixes]
Signed-off-by: Alexander Graf <agraf@suse.de>