ARM: dts: am57xx-beagle-x15: Include the commercial grade thresholds

am57xx-beagle-x15 have commercial grade samples whose
thermal thresholds lower than dra7. Hence correcting the same.

Signed-off-by: Keerthy <j-keerthy@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>