[X86] Cleanup inconsistencies in our zext/sext vector patterns.

-Fix one place where we had a X86vzload64 but should have had
 X86vzload32.
-Make sure all patterns that have scalar_to_vector+loadi64 also
have scalar_to_vector+f64 to match 32-bit codegen.
-Add some bitcasts that were missing from patterns.
-Make sure that if we have a scalar_to_vector+load pattern
 we also have a vzload pattern.

We probably need some better canonicalization to avoid having
so many patterns.