rtlwifi: Create new routine to initialize the DM tables

Each of the drivers contains a routine that initializes the dm_digtable
member of the driver's private area. As a first step toward reducing the
size of the drivers, a copy of this driver is created in rtlwifi, and the
definitions of the parameters are moved there.

Signed-off-by: Larry Finger <Larry.Finger@lwfinger.net>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>