drm/amd/pm: fix pptable use-after-free

In the Linux kernel, the following vulnerability has been resolved: drm/amd/pm: fix pptable use-after-free amdgpu_dpm_get_pp_table() returns a pointer to a driver-owned power table after dropping adev->pm.mutex. The sysfs path then copies from that pointer. A concurrent pp_table write can replace and free the allocation during the copy, causing a use-after-free. Change the DPM interface to copy into caller-provided storage while the mutex is held. Keep the size-only query for attribute discovery without exposing the driver-owned pointer. (cherry picked from commit f6eed7acfd30099ef7baeb6ba45bb59daad80631)