drivers: ethernet: Optimize RxBD buffer configuration

The _nxp_enet_dma_buffer_section is configured to __nocache area.
That makes the RxPkt performance very low (<= 50Mbps). By defining
it to the cacheable area, the RxPkt performance is >10x better.

Example with Zperf:
DUT command - zperf udp download 5001
PC command - iperf -u -c 192.0.2.1 -p 5001 -b 800M

Signed-off-by: Shrek Wang <shrek.wang@nxp.com>