KVM: arm64: nv: Handle HDFG[R|W]TR2_EL2 access from virtual EL2

This adds VNCR-capable HDFG[R|W]TR2_EL2 registers into enum vcpu_sysreg and
also handles their access from virtual EL2 environment.

Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>