amd-xgbe: Mask auto-negotiation interrupts in ISR

Currently the auto-negotiation interrupt handling disables the irq
instead of masking off the interrupts. This was done because the phy
library was originally used to read and write the PCS registers, which
could not be performed in interrupt context. Now that the phy library is
no longer used to read and write the PCS registers the interrupts can be
masked off in the interrupt service routine eliminating the need to call
disable_irq/enable_irq. This also requires changing the protection mutex
to a spinlock.

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