dpram_altera: make the dpram less technology dependant

read_during_write_mode_port parameter is only available on
M9K, M144K, M10K and M20K memory block types.

This parameter configure the type of new data behavior for
same-port RDW. When byte enable is applied, you can choose
to read old data, or ‘X’ on the masked byte.

As there is no RDW on this dpram in our case, we can safely
remove this parameter so the memory instanciation is compatible
with all kind of memory blocks.

More info: http://www.altera.com/literature/ug/ug_ram_rom.pdf

Also remove intended_device_family to make the instanciation
looks more generic.

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
Merge branch 'master' of github.com:fjullien/wb_sdram_ctrl
sync with stefan's repo