KVM: VMX: Add helpers to toggle/change a bit in VMCS execution controls

KVM: VMX: Add helpers to toggle/change a bit in VMCS execution controls

Expand the VMCS controls builder macros to generate helpers to change a
bit to the desired value, and use the new helpers when toggling APICv
related controls.

No functional change intended.

Suggested-by: Sean Christopherson <seanjc@google.com>
Signed-off-by: Dapeng Mi <dapeng1.mi@linux.intel.com>
Signed-off-by: Mingwei Zhang <mizhang@google.com>
[sean: rewrite changelog]
Tested-by: Xudong Hao <xudong.hao@intel.com>
Link: https://lore.kernel.org/r/20250806195706.1650976-27-seanjc@google.com
Signed-off-by: Sean Christopherson <seanjc@google.com>