lib_ppc: Move trap_init to occur earlier

Doing trap_init immediately once we're running from RAM
means we're no longer dependent on the physical location of
the flash on non-BookE platforms. Before trap_init, those
platforms switch to real mode and go to 0xfff00100 on exception.
After the switch, they go to 0x00000100  This makes it easier to
move the flash location.

Signed-off-by: Becky Bruce <becky.bruce@freescale.com>