Bluetooth: Use event masks instead of bits in controller and host

To avoid having to define a BIT64() macro in a public namespace, use
instead masks directly instead of bits, and also refactor the host code
so that it uses those instead of the earlier byte array with hardcoded
indices and masks.

Change-id: Ief03db616a96df65349d24289b62566a268ffdd0
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>