mv643xx_eth_get_config_reg() was reading the wrong register.
mv643xx_eth_set_config_reg() was or'ing instead of setting the
register.  These functions are trivial and both are called only from
mv643xx_eth_set_rx_mode() when changing to/from promiscuous mode.
Remove both functions and do the operations directly in
mv643xx_eth_set_rx_mode().

Also, maintain promiscuous mode setting across port resets.
Signed-off-by: Dale Farnsworth <dale@farnsworth.org>
Signed-off-by: Jeff Garzik <jgarzik@pobox.com>