Bluetooth: Add common Kconfig option to disable LE Data Length Update

This adds common option to disable support for LE Data Length Update
procedure in controller and host.
This will reduce flash usage by compiling out le_data_len_change
event handler that will never be called if controller has been
compiled with BT_CTLR_DATA_LENGTH option disabled.

Signed-off-by: Mariusz Skamra <mariusz.skamra@codecoup.pl>