KVM: arm64: nv: Enable HDFGRTR2_EL2 & HDFGWTR2_EL2 access from virtual EL2

This adds VNCR-capable HDFGRTR2_EL2 and HDFGWTR2_EL2 registers into enum
vcpu_sysreg and also enables their access from virtual EL2 environment.

Cc: Marc Zyngier <maz@kernel.org>
Cc: Oliver Upton <oliver.upton@linux.dev>
Cc: James Morse <james.morse@arm.com>
Cc: Suzuki K Poulose <suzuki.poulose@arm.com>
Cc: linux-arm-kernel@lists.infradead.org
Cc: kvmarm@lists.linux.dev
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Anshuman Khandual <anshuman.khandual@arm.com>