parisc: Improve cache flushing for PCXL in arch_sync_dma_for_cpu()

stable inclusion
from stable-v5.10.185
commit 3f7625e0862050dbeb00396d57a44b98103d8c47
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8L5XP

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=3f7625e0862050dbeb00396d57a44b98103d8c47



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[ Upstream commit 59fa1264 ]

Add comment in arch_sync_dma_for_device() and handle the direction flag in
arch_sync_dma_for_cpu().

When receiving data from the device (DMA_FROM_DEVICE) unconditionally
purge the data cache in arch_sync_dma_for_cpu().

Signed-off-by: Helge Deller <deller@gmx.de>
Signed-off-by: Sasha Levin <sashal@kernel.org>
Signed-off-by: sanglipeng <sanglipeng1@jd.com>