KVM: x86: support XSAVES usage in the host

KVM: x86: support XSAVES usage in the host

Userspace is expecting non-compacted format for KVM_GET_XSAVE, but
struct xsave_struct might be using the compacted format.  Convert
in order to preserve userspace ABI.

Likewise, userspace is passing non-compacted format for KVM_SET_XSAVE
but the kernel will pass it to XRSTORS, and we need to convert back.

Fixes: f31a9f7c71691569359fa7fb8b0acaa44bce0324
Cc: Fenghua Yu <[email protected]>
Cc: [email protected]
Cc: H. Peter Anvin <[email protected]>
Tested-by: Nadav Amit <[email protected]>
Reviewed-by: Radim Krčmář <[email protected]>
Signed-off-by: Paolo Bonzini <[email protected]>