Revert "drm/amdgpu: use the kernel zone memory size as the max remote memory in amdgpu"

Revert "drm/amdgpu: use the kernel zone memory size as the max remote memory in amdgpu"

This reverts commit 8658db04b1826d80ef70586f7484b7cc3b691cce.

This breaks on systems with huge amounts of system memory as we do not have
enough vram to store the page tables.  Additionally, this is less of an issue
with the recent gtt manager changes.

Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>