Remove pandaboard u-boot port.
It seems that omap4 boards has been removed from u-boot in 2024.10 release.
https://github.com/u-boot/u-boot/commit/1104cd616fef3111f851f7058511e45c3081f8cf
Related review to remove OMAP4 code in src: https://reviews.freebsd.org/D49661