[X86][Driver] Move mno-gather/mno-scatter from m_x86_Features_Group to m_Group. NFCI (#65457)

m_x86_Features_Group always turn `mno-xxxx` into `-target-feature
-xxxx`. In this case, we don't have `-gather/-scatter` but
`+prefer-no-gather/scatter`.

This patch solves unexpected warning when using
`mno-gather/mno-scatter`:
```
'-gather' is not a recognized feature for this target (ignoring feature)
'-scatter' is not a recognized feature for this target (ignoring feature)
```

Author: phoebewang

clang/include/clang/Driver/Options.td

@@ -5846,9 +5846,9 @@ def mretpoline_external_thunk : Flag<["-"], "mretpoline-external-thunk">, Group<
 def mno_retpoline_external_thunk : Flag<["-"], "mno-retpoline-external-thunk">, Group<m_x86_Features_Group>;
 def mvzeroupper : Flag<["-"], "mvzeroupper">, Group<m_x86_Features_Group>;
 def mno_vzeroupper : Flag<["-"], "mno-vzeroupper">, Group<m_x86_Features_Group>;
-def mno_gather : Flag<["-"], "mno-gather">, Group<m_x86_Features_Group>,
+def mno_gather : Flag<["-"], "mno-gather">, Group<m_Group>,
                  HelpText<"Disable generation of gather instructions in auto-vectorization(x86 only)">;
-def mno_scatter : Flag<["-"], "mno-scatter">, Group<m_x86_Features_Group>,
+def mno_scatter : Flag<["-"], "mno-scatter">, Group<m_Group>,
                   HelpText<"Disable generation of scatter instructions in auto-vectorization(x86 only)">;
 } // let Flags = [TargetSpecific]