(PRELIMINARY) arm64: Update headers for nested virt

Update the kernel headers to include the preliminary nested virt
additions, as taken from Marc's arm-platforms.git/kvm-arm64/nv-6.7-WIP
branch.

Should be replaced with the real headers from the then-mainline Linux
tree, once full NV support gets merged.

Signed-off-by: Andre Przywara <andre.przywara@arm.com>