PR target/83663 - Revert r255946
* config/aarch64/aarch64.c (aarch64_expand_vector_init): Modify code
generation for cases where splatting a value is not useful.
* simplify-rtx.c (simplify_ternary_operation): Simplify vec_merge
across a vec_duplicate and a paradoxical subreg forming a vector
mode to a vec_concat.