net: stmmac: dwmac1000: Disable ACS if enhanced descs are not used

ACS (auto PAD/FCS stripping) removes FCS off 802.3 packets (LLC) so that
there is no need to manually strip it for such packets. The enhanced DMA
descriptors allow to flag LLC packets so that the receiving callback can
use that to strip FCS manually or not. On the other hand, normal
descriptors do not support that.

Thus in order to not truncate LLC packet ACS should be disabled when
using normal DMA descriptors.

Fixes: 47dd7a54

 ("net: add support for STMicroelectronics Ethernet controllers.")
Signed-off-by: Remi Pommarel <repk@triplefau.lt>
Signed-off-by: David S. Miller <davem@davemloft.net>