ANDROID: pkvm: vmx: Handle hlt vmexit

The hlt vmexit is handled by the pkvm hypervisor to skip the
instruction. Then return back to the host KVM to emulate hlt by blocking
the vcpu thread.

Bug: 391539939
Test: pKVM works
Upstream-Task: 402758258

Change-Id: Ib7e12d420264d9c3f503b0a2999c5b04e8c315bc
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>
Signed-off-by: Dmytro Maluka <dmaluka@google.com>