powerpc/sbc8641: drop bogus PHY IRQ entries from DTS file

This file was originally cloned off of the MPC8641D-HPCN reference
platform, which actually had a PHY IRQ line connected. However this
board does not. The bogus entry was largely inert and went undetected
until commit 321beec5 ("net: phy: Use
interrupts when available in NOLINK state") was added to the tree.

With the above commit, the board fails to NFS boot since it sits waiting
for a PHY IRQ event that of course never arrives. Removing the bogus
entries from the DTS file fixes the issue.

Cc: Andrew Lunn <andrew@lunn.ch>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>