When CONFIG_BAND_6GHZ is disabled, compilation error is observed
due to the absence of the declaration of reg_convert_enum_to_6g_idx
and reg_get_reg_maschan_lst_frm_6g_pwr_mode.
To fix this issue, add static declarations for
reg_convert_enum_to_6g_idx and reg_get_reg_maschan_lst_frm_6g_pwr_mode
when CONFIG_BAND_6GHZ is disabled.
Change-Id: I616de6cd2630be1897da6cd87a29569e51bf058e
CRs-Fixed: 3131119