arch: Remove leftovers from prism54 wireless driver

This driver was removed so remove all references to it.

Fixes: d249ff28 ("intersil: remove obsolete prism54 wireless driver")
Signed-off-by: Alexandre Ghiti <alexandre.ghiti@canonical.com>
Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>