Masked gemv (#1211)

Author: jagrit06

mlx/backend/metal/kernels/CMakeLists.txt

@@ -37,6 +37,7 @@ endfunction(build_kernel)
 build_kernel(arg_reduce)
 build_kernel(conv steel/conv/params.h)
 build_kernel(gemv steel/utils.h)
+build_kernel(gemv_masked steel/utils.h)
 build_kernel(layer_norm)
 build_kernel(random)
 build_kernel(rms_norm)