powerpc/configs/powernv: Add IGB=y

Some powernv machines use IGB for networking, so build the driver in to
enable net booting such machines.
Suggested-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230420052149.1328094-1-mpe@ellerman.id.au

arch/powerpc/configs/powernv_defconfig

@@ -170,6 +170,7 @@ CONFIG_S2IO=m
 CONFIG_E100=y
 CONFIG_E1000=y
 CONFIG_E1000E=y
+CONFIG_IGB=y
 CONFIG_IXGB=m
 CONFIG_IXGBE=m
 CONFIG_I40E=m