mpc83xx: sbc8349 - make enabling PCI more user friendly

Prior to this commit, to enable PCI, you had to go manually
edit the board config header, which isn't really user friendly.
This adds the typical PCI make targets to the toplevel Makefile
in accordance with what is being done with other boards.

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