ANDROID: gzvm driver: fix UAF issue

When a VM is destroyed, it also triggers the destruction of its
associated vCPUs. However, this process can potentially result
in use-after-free issue. To address this, we add kref (kernel
reference counter) to trace the  userspace events. Once the
vCPU is destroyed, gzvm release all the resources.

(e.g. Open VM_FD -> Open VCPU_FD -> Close VM_FD -> VCPU_RUN)

Bug: 444329675
Signed-off-by: kevenny hsieh <kevenny.hsieh@mediatek.com>
Signed-off-by: Liju Chen <liju-clr.chen@mediatek.com>
Change-Id: Idb7dd29da2515500ff4348940478443085bded4e