rs6000: Rename patterns for vec_widen_<s>mult_even/odd_<mode>
* config/rs6000/altivec.md (vec_widen_umult_even_v16qi): Rename
from altivec_vmuleub.
(vec_widen_smult_even_v16qi): Rename from altivec_vmulesb.
(vec_widen_umult_even_v8hi): Rename from altivec_vmuleuh.
(vec_widen_smult_even_v8hi): Rename from altivec_vmulesh.
(vec_widen_umult_odd_v16qi): Rename from altivec_vmuloub.
(vec_widen_smult_odd_v16qi): Rename from altivec_vmulosb.
(vec_widen_umult_odd_v8hi): Rename from altivec_vmulouh.
(vec_widen_smult_odd_v8hi): Rename from altivec_vmulosh.
* config/rs6000/rs6000-builtin.def: Update pattern names to match.