The approved trademark name is Wi-Fi so update references to WiFi and
other spellings to Wi-Fi in documentation and Kconfig help strings.
(Note that use of spelling variatios of "wifi" in module names, CONFIG
names, link names and such are untouched.)
https://www.wi-fi.org/
Signed-off-by: David B. Kinder <david.b.kinder@intel.com>