ARM: dts: tegra: Fix missing card detection in Trimslice µSD card slot

Card insertion and removal currently goes undetected. AFAIK there's no
way to generate interrupts on card changes in this slot, so use polling.

Signed-off-by: Rask Ingemann Lambertsen <rask@formelder.dk>
Signed-off-by: Thierry Reding <treding@nvidia.com>