[aarch64] Use neoversen1 tuning struct for -mcpu=cortex-a76

[aarch64] Use neoversen1 tuning struct for -mcpu=cortex-a76

The neoversen1 tuning struct gives better performance on the Cortex-A76, so use that.
The only difference from the current tuning is the function and label alignment settings.

This gives about 1.3% improvement on SPEC2006 int and 0.3% on SPEC2006 fp.

        * config/aarch64/aarch64-cores.def (cortex-a76): Use neoversen1 tuning
        struct.

From-SVN: r274511