drm/amdgpu: update retry times for psp vmbx wait

Increase the retry loops and replace the constant number with macro.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>