rtl8192su: add AR-7284WnA and B rtl8192su driver

This special driver was discovered by:
	José Vázquez <ppvazquezfer@gmail.com>
some time ago. It features several improvements
like AP mode and softmac over the current vendor
driver. Therefore it should be the blueprint for
future developement.

Signed-off-by: Christian Lamparter <chunkeey@googlemail.com>