mpc83xx: U-Boot support for Wind River SBC8349

I've redone the SBC8349 support to match git-current, which
incorporates all the MPC834x updates from Freescale since the 1.1.6
release,  including the DDR changes.

I've kept all the SBC8349 files as parallel as possible to the
MPC8349EMDS ones for ease of maintenance and to allow for easy
inspection of what was changed to support this board.  Hence the SBC8349
U-Boot has FDT support and everything else that the MPC8349EMDS has.

Fortunately the Freescale updates added support for boards using CS0,
but I had to change spd_sdram.c to allow for board specific settings for
the sdram_clk_cntl (it is/was hard coded to zero, and that remains the
default if the board doesn't specify a value.)

Hopefully this should be mergeable as-is and require no whitespace
cleanups or similar, but if something doesn't measure up then let me
know and I'll fix it.

Thanks,
Paul.