arch/powerpc: add fsl e5500 and e6500 support

Add Freescale E5500 and E6500 core support.
These can go in 32 or 64-bit mode.
I'm not aware of these being able to boot in LE mode so filter that out
until we get some feedback on it.

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Reviewed-by: "Matt Weber" <matthew.weber@rockwellcollins.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>