rtlwifi: Rework Kconfig

As the number of drivers in the rtlwifi family has grown, the Kconfig
section for them has grown unwieldy. This change has two effects: (1)
Variable RTLWIFI_DEBUG is documented, and (2) the entries for the
drivers that depend on RTLWIFI are indented.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: John W. Linville <linville@tuxdriver.com>