staging: fsl-dpaa2/eth: Use generic irq handler

For the link state interrupt, we used a dummy non-threaded
irq handler, which had the same implementation as the generic
irq_default_primary_handler() function.

Give up on using our own irq handler and let the kernel use
the generic one instead.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>