default or selected kernelversion does not have config value CONFIG_DRM_AMDGPU_GART_DEBUGFS.
Result is shown for kernelversion 6.9.5

Allow GART access through debugfs


Linux Kernel Configuration
└─>Device Drivers
└─>Graphics support
└─>Allow GART access through debugfs
In linux kernel since version 4.1 (release Date: 2015-06-21)  
Selecting this option creates a debugfs file to inspect the mapped
pages. Uses more memory for housekeeping, enable only for debugging.