fec: don't enable irqs in hard irq context

fec_enet_mii, fec_enet_rx and fec_enet_tx are both only called by
fec_enet_interrupt in interrupt context.  So they must not use
spin_lock_irq/spin_unlock_irq.

This fixes:
	WARNING: at kernel/lockdep.c:2140 trace_hardirqs_on_caller+0x130/0x194()
	...

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Greg Ungerer <gerg@uclinux.org>
Cc: Ben Hutchings <ben@decadent.org.uk>
Cc: Patrick McHardy <kaber@trash.net>
Cc: Sascha Hauer <s.hauer@pengutronix.de>
Cc: Matt Waddel <Matt.Waddel@freescale.com>
Cc: netdev@vger.kernel.org
Cc: Tim Sander <tim01@vlsi.informatik.tu-darmstadt.de>
Acked-by: Greg Ungerer <gerg@uclinux.org>
Signed-off-by: David S. Miller <davem@davemloft.net>