KVM: arm64: Load VPIDR_EL2 with the VM's MIDR_EL1 value

KVM: arm64: Load VPIDR_EL2 with the VM's MIDR_EL1 value

Userspace will soon be able to change the value of MIDR_EL1. Prepare by
loading VPIDR_EL2 with the guest value for non-nested VMs.

Since VPIDR_EL2 is set for any VM, get rid of the NV-specific cleanup of
reloading the hardware value on vcpu_put(). And for nVHE, load the
hardware value before switching to the host.

Link: https://lore.kernel.org/r/20250225005401.679536-4-oliver.upton@linux.dev
Signed-off-by: Oliver Upton <oliver.upton@linux.dev>