ANDROID: BACKPORT: KVM: arm64: Use guest VMID as owner id

We currently track page-ownership in nVHE protected mode with a rather
coarse granularity -- all guests share a unique owner id. But a finer
grain tracking will be useful soon, to e.g. handle host stage-2 faults
caused by an access to guest memory. To prepare the ground for this,
let's use the guest VMIDs as owner ids, hence allowing to distinguish
between all of them. This only works since the pKVM EL2 hypervisor
guarantees the stability of the VMIDs for the entire lifetime of a guest
VM. This will need some rework when/if we attempt to run more than 255
guests concurrently in protected mode as we'll have to handle VMID
rollovers, but there is no clear need for now, so let's keep it simple
to start.

Signed-off-by: Quentin Perret <qperret@google.com>
[willdeacon@: Update constants in mem_protect.h]
Bug: 209580772
Change-Id: I5c5c8061617d7dc481ae5e25a0391b306aabbd8c
Signed-off-by: Will Deacon <willdeacon@google.com>