powerpc/pseries/ddw: Revert "Extend upper limit for huge DMA window for persistent...

powerpc/pseries/ddw: Revert "Extend upper limit for huge DMA window for persistent memory"

[ Upstream commit 2d33f5504490a9d90924476dbccd4a5349ee1ad0 ]

This reverts commit 54fc3c681ded9437e4548e2501dc1136b23cfa9a
which does not allow 1:1 mapping even for the system RAM which
is usually possible.

Signed-off-by: Alexey Kardashevskiy <aik@ozlabs.ru>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20211108040320.3857636-2-aik@ozlabs.ru
Signed-off-by: Sasha Levin <sashal@kernel.org>