xparameters should not be needed by anything but virtex platform code.
Move it from include/asm-ppc/ to platforms/4xx/xparameters/

This is preparing for work to remove xparameters from the dependancy tree
for most c files.  xparam changes should not cause a recompile of the world.
Instead, drivers should get device info from the platform bus (populated
by the boot code)
Signed-off-by: NGrant C. Likely <grant.likely@secretlab.ca>
Signed-off-by: NPaul Mackerras <paulus@samba.org>