KVM: arm64: vgic-v5: Add missing trap handing for NV triage

KVM: arm64: vgic-v5: Add missing trap handing for NV triage

As things stand, there is no support for Nested Virt with GICv5 guests
yet. However, this is coming and therefore we need to be able to
correctly triage the traps when running with NV.

Add the missing fgtreg lookups required for that to
triage_sysreg_trap(). These are specific to the FGT regs added as part
of GICv5:
   * ICH_HFGRTR_EL2
   * ICH_HFGWTR_EL2
   * ICH_HFGITR_EL2

Fixes: 9d6d9514c08f ("KVM: arm64: gic-v5: Support GICv5 FGTs & FGUs")
Link: https://sashiko.dev/#/patchset/20260319154937.3619520-1-sascha.bischoff%40arm.com
Signed-off-by: Sascha Bischoff <sascha.bischoff@arm.com>
Reviewed-by: Joey Gouly <joey.gouly@arm.com>
Link: https://lore.kernel.org/r/20260520091949.542365-11-maz@kernel.org
Signed-off-by: Marc Zyngier <maz@kernel.org>