Integrate meta-seco-edgehog-things/niccolor/mkimage-px30

Commit: https://git.seco.com/edgehog/layers/seco/meta-seco-edgehog-things/-/commit/f8acd900a99dc569db89e338f8d41a745dc9730f

[U-BOOT][MKIMAGE][PX30] Use specific mkimage for px30

After passing to u-boot-seco-rk branch next, using the usual mkimage will compile seco_boot.scr in a way that is not readable for u-boot, resulting in a non bootable device