microblaze: Kill NET_SKB_PAD and NET_IP_ALIGN overrides.

NET_IP_ALIGN defaults to 2, no need to override.

NET_SKB_PAD is now 64, which is much larger than microblaze's
L1_CACHE_SIZE so no need to override that either.

Signed-off-by: David S. Miller <davem@davemloft.net>