Staging: rtxx70: merge rt3070 with rt2870

* remove RT30xx ifdefs
* add -DRT3070 to rt2870's EXTRA_CFLAGS
* because of changes in the way that hardware is initialized/accessed
  rt3070 driver's firmware should be now also used by rt2870 driver
  (this is also done by newer out-of-tree vendor driver versions, i.e.
  2.1.0.0, historically in-kernel driver was based on 1.4.0.0 version)
* change RT28xx_CHIP_NAME to RTxx70
* update rt2870's help entry text
* add MODULE_ALIAS("rt3070sta") to rt2870
* update rt3070's dependencies

Signed-off-by: Bartlomiej Zolnierkiewicz <bzolnier@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>