drm/etnaviv: stop abusing mmu_context as FE running marker

stable inclusion
from stable-5.10.68
commit c63e6e0951ff4ab021947b834db37f591781ee28
bugzilla: 182671 https://gitee.com/openeuler/kernel/issues/I4EWUH

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git/commit/?id=c63e6e0951ff4ab021947b834db37f591781ee28



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commit 23e0f5a5 upstream.

While the DMA frontend can only be active when the MMU context is set, the
reverse isn't necessarily true, as the frontend can be stopped while the
MMU state is kept. Stop treating mmu_context being set as a indication that
the frontend is running and instead add a explicit property.

Cc: stable@vger.kernel.org # 5.4
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Michael Walle <michael@walle.cc>
Tested-by: Marek Vasut <marex@denx.de>
Reviewed-by: Christian Gmeiner <christian.gmeiner@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Chen Jun <chenjun102@huawei.com>
Acked-by: Weilong Chen <chenweilong@huawei.com>

Signed-off-by: Chen Jun <chenjun102@huawei.com>
Signed-off-by: Zheng Zengkai <zhengzengkai@huawei.com>