powerpc: Remove ucache_bsize

ppc601 and e200 were the users of ucache_bsize.
ppc601 and e200 are now gone.

Remove ucache_bsize.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/288b6048597c0fdc495b203fda57a223d89499d2.1605589460.git.christophe.leroy@csgroup.eu