staging: mt7621-pci: remove dead code derived to not use custom reads and writes

Driver is using now pci subsystem generics reads and writes and requesting
bus resources without using legacy code functions. Because of this there is
a lot of dead code that can be removed.

Signed-off-by: Sergio Paracuellos <sergio.paracuellos@gmail.com>
Tested-by: NeilBrown <neil@brown.name>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>