KVM: x86/mmu: Wrap sanity check on number of TDP MMU pages with KVM_PROVE_MMU

Wrap the TDP MMU page counter in CONFIG_KVM_PROVE_MMU so that the sanity
check is omitted from production builds, and more importantly to remove
the atomic accesses to account pages.  A one-off memory leak in production
is relatively uninteresting, and a WARN_ON won't help mitigate a systemic
issue; it's as much about helping triage memory leaks as it is about
detecting them in the first place, and doesn't magically stop the leaks.
I.e. production environments will be quite sad if a severe KVM bug escapes,
regardless of whether or not KVM WARNs.

Signed-off-by: Sean Christopherson <seanjc@google.com>
Message-ID: <20250315023448.2358456-1-seanjc@google.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>