Wifi: Reorganize wifi bands definition

This CL reorganizes wifi bands definition to be represented as
a bit-mask rather than arbitrary values.
This is useful for making it scalable for adding new bands. This
is a prep step before adding 6GHz band support.

Bug: 139354972
Test: Manual
Change-Id: I95b359ed05d429abc81faa726bc6a282b3a3e329