sw64: gpu: use memset_io and memcpy_toio/fromio for iomem

Sunway inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I5GDKC



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This commit complements commit afe00ca0 ("sw64: gpu: correct
low-level mmio memset/memcpy direct calls").

Signed-off-by: Zhou Xuemei <zhouxuemei@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>