powerpc/mpc8xxx: move LAW code into arch/powerpc/cpu/mpc8xxx

It's arch code and not a driver, so move it where it belongs.  When it
originally went into drivers/misc there was no 8xxx CPU directory.

This will make new-SPL support a little easier since we can keep the CPU
stuff together and not need to pull stuff in from drivers/misc.

Signed-off-by: Scott Wood <scottwood@freescale.com>
Cc: Andy Fleming <afleming@freescale.com>