net: remove am79c961a driver

This driver was only used on the EBSA110 platform, which is now
getting removed, so the driver is no longer needed either.

Acked-by: Russell King <rmk+kernel@armlinux.org.uk>
Acked-by: Jakub Kicinski <kuba@kernel.org>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>