KVM: arm64: Hoist NV+SVE check into KVM_ARM_VCPU_INIT ioctl handler

Move the feature check out of kvm_reset_vcpu() so we can make the
function succeed uncondtitionally.

Link: https://lore.kernel.org/r/20230920195036.1169791-7-oliver.upton@linux.dev


Signed-off-by: Oliver Upton <oliver.upton@linux.dev>