NET: move legacy enc28j60.c to sidetrack as enc28j60_lpc2292.c

This patch is required before the upcoming new enc28j60 driver
using SPI framework patch can be applied:
- Move legacy enc28j60.c to enc28j60_lpc2292.c.
- Change Makefile and the two affected boards' definition files.

Tested with ./MAKEALL ARM7 that both boards still compile.

Signed-off-by: Reinhard <Meyer&lt;info@emk-elektronik.de>
Signed-off-by: Ben Warren <biggerbadderben@gmail.com>