powerpc/platforms: Move files from 4xx to 44x

Only 44x uses 4xx now, so only keep one directory.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/20240628121201.130802-7-mpe@ellerman.id.au