bazel: including bootloader targets in `link_extra_lib` results in a dependency cycle

[cramertj]

The bazel bootloader targets (e.g. @@pico-sdk~//src/rp2040/boot_stage2:boot_stage2_elf_actual) get built with link_extra_lib in their deps, so including them in the link_extra_lib list for other binaries causes a dependency cycle. This cycle should be broken by removing link_extra_lib dependencies when building bootloader targets.

PR incoming.

[kilograham]

merged into develop