amd-xgbe: Fix IRQ processing when running in single IRQ mode

When running in single IRQ mode, the additional IRQ routines were being
skipped because only the XGMAC interrupt status was being checked.
Update the code so that the additional IRQ routines are checked whenever
an interrupt is received.

Signed-off-by: Tom Lendacky <thomas.lendacky@amd.com>
Signed-off-by: David S. Miller <davem@davemloft.net>