arm: dts: k3-*-binman: Move to using ti-dm entry type

arm: dts: k3-*-binman: Move to using ti-dm entry type

Move the DM entry in tispl.bin FIT image from default fetching an
external blob entry to fetching using ti-dm entry type. This way, the
DM entry will be populated by the TI_DM pathname if provided. Else it
will resort to the ti-dm.bin file.

Signed-off-by: Neha Malcom Francis <n-francis@ti.com>
Reviewed-by: Andrew Davis <afd@ti.com>
Reviewed-by: Simon Glass <sjg@chromium.org>