rtl818x: move rtl8180 and rtl8187 to separate subdirectories

These drivers share one header file, but nothing else.  Worse, both
drivers use the rtl8225 part with different register settings.  The
results has been some ugly naming -- let's simplify that.

Signed-off-by: John W. Linville <linville@tuxdriver.com>
Acked-by: Hin-Tak Leung <htl10@users.sourceforge.net>
Acked-by: Larry Finger <Larry.Finger@lwfinger.net>
Acked-by: Herton Ronaldo Krzesinski <herton@mandriva.com.br>