Since commit 9e849f23 ("powerpc/mm/32s: use generic mmu_mapin_ram()
for all blocks.") it is possible to map all blocks as RAM on any PPC32.

Remove related restrictions.

And remove call to wii_memory_fixups() which doesn't do anything else
than checks since commit 160985f3 ("powerpc/wii: remove
wii_mmu_mapin_mem2()")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/fc9a5b8ef49f6eb86e970d4c7ccfba9b407fd4eb.1661938317.git.christophe.leroy@csgroup.eu