boot/uboot: remove BR2_TARGET_UBOOT_TI_K3_DM_SOCNAME

Previoulsy (without binman), when a TI K3 SoC using Combined binary
with a split firmware boot method was used (am62ax or am62x) [1], the
user had to select BR2_TARGET_UBOOT_NEEDS_TI_K3_DM in the defconfig
to provide Device Manager firmware provided by ti-k3-boot-firmware.

With binman, this option is no longer necessary since
ti-k3-boot-firmware package is already in the u-boot dependency and the
path to DM and SYSFW binaries are provided by BINMAN_INDIRS.

We are going to remove ti-k3-image-gen, so binman is now mandatory on
all TI K3 SoCs.

[1] https://gitlab.com/buildroot.org/buildroot/-/commit/52ce606c05ee3ac869f8087292bc3dbb0d25b79b

Reviewed-by: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Romain Naour <romain.naour@smile.fr>
2 files changed