KVM: x86: Shrink struct kvm_pmu

Move the 'version' member to the beginning of the structure to reuse an
existing hole instead of introducing another one.

This allows us to save 8 bytes for 64 bit builds.

Signed-off-by: Mathias Krause <minipli@grsecurity.net>
Link: https://lore.kernel.org/r/20230217193336.15278-2-minipli@grsecurity.net
Signed-off-by: Sean Christopherson <seanjc@google.com>