net: qcom/emac: claim the irq only when the device is opened

During reset, functions emac_mac_down() and emac_mac_up() are called,
so we don't want to free and claim the IRQ unnecessarily.  Move those
operations to open/close.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
Reviewed-by: Lino Sanfilippo <LinoSanfilippo@gmx.de>
Signed-off-by: David S. Miller <davem@davemloft.net>