KVM: arm64: Enumerate SVE register indices for KVM_GET_REG_LIST

This patch includes the SVE register IDs in the list returned by
KVM_GET_REG_LIST, as appropriate.

On a non-SVE-enabled vcpu, no extra IDs are added.

On an SVE-enabled vcpu, the appropriate number of slice IDs are
enumerated for each SVE register, depending on the maximum vector
length for the vcpu.

Signed-off-by: Dave Martin <Dave.Martin@arm.com>