Wifi: Add definitions for bands frequency boundries

Channel frequency ranges for the three bands (2.4G, 5G, and 6G) are used
in different places with separate definitions or via literal numbers.
Also, the values are not accurate and sometimes not consistent.

This commit defines those ranges in a single place for use of other
classes. It also adds some utility methods that use those definitions.

Bug: 153896822
Test: atest android.net.wifi
Change-Id: Ifd19e245fd808c06d48d7557e30be3e92a9e7ec5