ANDROID: pkvm: vmx: Switch the spec ctrl MSR when switching to/from the host

The spec ctrl MSR controls control various speculative execution
mitigations and it is passthrough to the host VM. To make sure the pkvm
hypervisor runs with the desired spec ctrl MSR, restoring the spec ctrl
with the pkvm's value after exiting from the host VM and restoring with
the host VM's value before entering the host VM.

Bug: 420681877
Upstream-Task: 402758258

Change-Id: I19d6c0da76fd174fee21defd8365ef03b5c01383
Signed-off-by: Chuanxiao Dong <chuanxiao.dong@intel.com>