KVM: arm64: Hoist SVE check into KVM_ARM_VCPU_INIT ioctl handler

Test that the system supports SVE before ever getting to
kvm_reset_vcpu().

Link: https://lore.kernel.org/r/20230920195036.1169791-4-oliver.upton@linux.dev


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