drm: amdgpu: radeon: disable cache flush workaround for LoongArch and Loongson64

[MingcongBai]

This workaround causes instability for LoongArch/Loongson (MIPS) devices based on the 7A1000/2000 chipset under heavy I/O load.

FIXME: Disable this workaround until we find a better fix (possibly in the platform-specific PCI code).

[deepin-ci-robot]

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[FlyGoat]

MACH_LOONGSON64 足以覆盖LA与MIPS的受影响平台了。

[deepin-ci-robot]

deepin pr auto review

关键摘要:

• 在AMDGPU的ring_emit_fence_gfx函数中，新增了条件编译指令来禁用针对LoongArch/Loongson (MIPS) 7A1000/2000芯片组的workaround，这有助于解决在重负载下的不稳定问题。
• 注释中提到“FIXME：禁用此workaround直到我们找到更好的解决方案（可能是在平台特定PCI代码中）”。这表明当前的workaround可能不是最优的，需要进一步探索解决方案。

是否建议立即修改:

• 是，建议立即修改以避免潜在的系统不稳定问题。同时，需要关注注释中提到的“FIXME”，确保问题得到及时解决，以保护系统的稳定性。

[MingcongBai]

MACH_LOONGSON64 足以覆盖LA与MIPS的受影响平台了。

了解，已据此修改