arm: dts: am625_sk: Switch to OF_UPSTREAM

arm: dts: am625_sk: Switch to OF_UPSTREAM

Enable OF_UPSTREAM for am625-sk board. Remove DT files that
are now available in dts/upstream. Update the appended files based on
version of latest OF_UPSTREAM sync point (v6.10-rc1).

Signed-off-by: Nishanth Menon <nm@ti.com>
Reviewed-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Tested-by: Mattijs Korpershoek <mkorpershoek@baylibre.com>
Reviewed-by: Bryan Brattlof <bb@ti.com>
Reviewed-by: Dhruva Gole <d-gole@ti.com>