declaring port as array type

you cannot declare an array like that. First you need to declare the type and then create a signal of that type. In this case you will need to declare the array type in a package.

type my_array_t is array(2**sel_bits-1 downto 0) of bit_vector(data_width-1 downto 0);

--in the port

input : my_array_y;

The upshot of this is that you will need to decalre the generics as constants in the package also.