tiboot3/tispl: add BINMAN_INDIRS variable
On ti-u-boot-2023.04, we switched to binman for generating the images. In order for binman to find the appropriate firmwares, we should pass the BINMAN_INDIRS environment variable when building U-Boot.
[1] https://git.ti.com/cgit/ti-u-boot/ti-u-boot/tree/doc/board/ti/am62x_sk.rst?h=ti-u-boot-2023.04#n168 Suggested-by: Guillaume La Roque glaroque@baylibre.com Signed-off-by: Mattijs Korpershoek mkorpershoek@baylibre.com