drm/amdgpu: use GTT only as fallback for VRAM|GTT

Try to fill up VRAM as well by setting the busy flag on GTT allocations.

This fixes the issue that when VRAM was evacuated for suspend it's never
filled up again unless the application is restarted.

Signed-off-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Zack Rusin <zack.rusin@broadcom.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240229134003.3688-2-christian.koenig@amd.com