powerpc/mm: Remove dcache flush from memory remove.

We added dcache flush on memory add/remove in commit
fb5924fd ("powerpc/mm: Flush cache on memory hot(un)plug") to
handle crashes on GPU hotplug. Instead of adding dcache flush in
generic memory add/remove routine which is used even for regular
memory, we should handle these devices specific flush in the device
driver code.

memtrace did handle this in the driver and that was removed by commit
7fd6641d ("powerpc/powernv/memtrace: Let the arch hotunplug code
flush cache"). This patch reverts that commit.

The dcache flush in memory add was removed by commit
ea458eff ("powerpc: Don't flush caches when adding memory") which
I don't think is correct. The reason why we require dcache flush in
memtrace is to make sure we don't have a dirty cache when we remap a
pfn to cache inhibited. We should do that when the memtrace module
removes the memory and make the pfn available for HTM traces to map it
as cache inhibited.

The other device mentioned in commit fb5924fd ("powerpc/mm: Flush
cache on memory hot(un)plug") is nvlink device with coherent memory.
The support for that was removed in commit
7eb3cf76 ("powerpc/powernv: remove unused NPU DMA code") and
commit 25b2995a ("mm: remove MEMORY_DEVICE_PUBLIC support")

Signed-off-by: Aneesh Kumar K.V <aneesh.kumar@linux.ibm.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/20210203045812.234439-3-aneesh.kumar@linux.ibm.com