sbc8349: tidy up Makefile to use new configuration script.

Commit 804d83a5 allows us to move all the configuration
variation tweaks out of the top level Makefile and down
into the board config header.  This takes advantage of
that for the sbc8349 board.

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Kim Phillips <kim.phillips@freescale.com>