drm/amdgpu: Rework KFD memory max limits

To allow bigger allocations specially on systems such as GFXIP 9.4.3
that use GTT memory for VRAM allocations, relax the limits to
maximize ROCm allocations.

Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Rajneesh Bhardwaj <rajneesh.bhardwaj@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>