unify softmax + quantized, more dispatches to simd quantized mm

Author: awni

Diff for: mlx/backend/accelerate/CMakeLists.txt

@@ -3,6 +3,4 @@ target_sources(
   PRIVATE ${CMAKE_CURRENT_SOURCE_DIR}/conv.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/matmul.cpp
           ${CMAKE_CURRENT_SOURCE_DIR}/primitives.cpp
-          ${CMAKE_CURRENT_SOURCE_DIR}/quantized.cpp
-          ${CMAKE_CURRENT_SOURCE_DIR}/reduce.cpp
-          ${CMAKE_CURRENT_SOURCE_DIR}/softmax.cpp)
+          ${CMAKE_CURRENT_SOURCE_DIR}/reduce.cpp)