drivers: net: cpsw: remove disable_irq/enable_irq as irq can be masked from cpsw itself

CPSW interrupts can be disabled by masking CPSW interrupts and
clearing interrupt by writing appropriate EOI. So removing all
disable_irq/enable_irq as discussed in [1]

[1] http://patchwork.ozlabs.org/patch/492741/



Signed-off-by: Mugunthan V N <mugunthanvnm@ti.com>
Signed-off-by: David S. Miller <davem@davemloft.net>