powerpc: drop MPC8272-ADS and PowerQUICC II FADS shared code.

With the two platforms depending on this shared code, and no others,
we can remove the orphaned code and Kconfigs

Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20230224204959.17425-4-paul.gortmaker@windriver.com