qcacld-3.0: Convert SME code legacy channel ID usage

1) Change csr_get_cfg_valid_channels's code to make it
   use channel frequencies directly to calculate a
   valid channel list.

2) Add kernel-doc for csr_get_cfg_valid_channels.

3) Remove the definition, declaration and usage of
   csr_get_cfg_valid_freq as csr_get_cfg_valid_channels
   does exactly the same job.

Change-Id: I6745cb2220bf9387c64ac8c271297cb89f821ab3
CRs-Fixed: 2560091
3 files changed