TQM8xx* boards: set larger SMC Rx buffer len

Commit 2b3f12c2 added support for configurable SMC Rx buffer length on
8xx systems. Enable this feature on TQM8xx* based boards.

This fixes the problem that pasting text in the middle of a line
(i. e. inserting in edit mode) did not work - only the first two
characters got inserted, the rest was lost.

Signed-off-by: Wolfgang Denk <wd@denx.de>