[POWERPC] bootwrapper: Revert ps3 binary flag usage, and remove .bin suffix

The ps3 target produces two images, and the binary one is not the
"primary" image that corresponds to the -o flag; thus, it no longer
uses the generic binary flag.

On platforms which do use the binary flag, it no longer produces a
.bin suffix, so that the output file matches what was passed to the -o flag.

This should fix the zImage ln problems for the ps3 target.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Acked-by: Geert Uytterhoeven <Geert.Uytterhoeven@sonycom.com>
Signed-off-by: Paul Mackerras <paulus@samba.org>