KVM: x86/mmu: Stop kicking vCPUs to sync the dirty log when PML is disabled

Stop kicking vCPUs in kvm_arch_sync_dirty_log() when PML is disabled.
Kicking vCPUs when PML is disabled serves no purpose and could
negatively impact guest performance.

This restores KVM's behavior to prior to 5.12 commit a018eba5 ("KVM:
x86: Move MMU's PML logic to common code"), which replaced a
static_call_cond(kvm_x86_flush_log_dirty) with unconditional calls to
kvm_vcpu_kick().

Fixes: a018eba5 ("KVM: x86: Move MMU's PML logic to common code")
Signed-off-by: David Matlack <dmatlack@google.com>
Link: https://lore.kernel.org/r/20231016221228.1348318-1-dmatlack@google.com


Signed-off-by: Sean Christopherson <seanjc@google.com>