arm: k3-am65x-iot2050: Use binman for tispl.bin for iot2050

Move to using binman to generate tispl.bin which is used to generate the
final flash.bin bootloader for iot2050 boards.

Cc: Jan Kiszka <jan.kiszka@siemens.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Neha Malcom Francis <n-francis@ti.com>