KVM: PPC: booke: category E.HV (GS-mode) support

KVM: PPC: booke: category E.HV (GS-mode) support

Chips such as e500mc that implement category E.HV in Power ISA 2.06
provide hardware virtualization features, including a new MSR mode for
guest state.  The guest OS can perform many operations without trapping
into the hypervisor, including transitions to and from guest userspace.

Since we can use SRR1[GS] to reliably tell whether an exception came from
guest state, instead of messing around with IVPR, we use DO_KVM similarly
to book3s.

Current issues include:
 - Machine checks from guest state are not routed to the host handler.
 - The guest can cause a host oops by executing an emulated instruction
   in a page that lacks read permission.  Existing e500/4xx support has
   the same problem.

Includes work by Ashish Kalra <[email protected]>,
Varun Sethi <[email protected]>, and
Liu Yu <[email protected]>.

Signed-off-by: Scott Wood <[email protected]>
[agraf: remove pt_regs usage]
Signed-off-by: Alexander Graf <[email protected]>
Signed-off-by: Avi Kivity <[email protected]>