staging: rtl8723au: Create rtl8723au_bt_intf.h

Use this header for declaring functions that are currently #ifdef'ed
out in the general code.

Start by moving BTDM_1Ant8723A() there and renaming it appropriately.

Signed-off-by: Jes Sorensen <Jes.Sorensen@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>