gianfar: Implement MAC reset and reconfig procedure

gianfar: Implement MAC reset and reconfig procedure

The main MAC config registers like: RCTRL/TCTRL, MRBLR,
MAXFRM, RXIC/TXIC, most fields of MACCFG1/2, should not
be changed on-the-fly, but at least after stopping the
DMA and disabling the Rx/Tx blocks and, for increased
reliability, after a MAC soft reset.

Impelement a complete MAC soft reset and reconfig procedure
following the latest HW advisories - gfar_mac_reset() - to
replace gfar_mac_init() and (the confusing) init_registers()
functions.

Factor out separate config functions for RCTRL and TCTRL,
insure programming order of the relevant config regs after
MAC soft reset.

Split gfar_hw_init() into gfar_mac_reset() and the remaining
global regs that don't need to be reconfigured after MAC soft
reset (FIFOCFG, ATTRELI, HW counters a.s.o).

As gfar_hw_init() now makes all the register writes @probe()
time, based on all the device flags and config options, it
must be moved further down, just before register_netdev(),
as the last config step when the config values are comitted
to HW.  Also, move netif_carrier_off() after register_netdev(),
because it has no effect if called before.

Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Signed-off-by: David S. Miller <davem@davemloft.net>