ls102xa: etsec: Use proper settings for BE BDs

Replace the DMACTRL[LE] hack with recommended settings
for ETSECDMAMCR to get the same end effect - obtaining
big-endian buffer descriptors and frame data for eTSEC.
The reset / default value for ETSECDMAMCR is preserved,
excepting the BD and FR bits which are cleared to enable
the BE mode in accordance with the H/W specifications.

Fixes: 52d00a81 "ls102xa: etsec: Add etsec support for LS102xA"
Signed-off-by: Claudiu Manoil <claudiu.manoil@freescale.com>
Acked-by: Alison Wang <alison.wang@freescale.com>
Tested-by: Alison Wang <alison.wang@freescale.com>
Reviewed-by: York Sun <yorksun@freescale.com>