Unlike most other Zephyr libraries, libkernel.a is not built as a
whole-archive.
This change also fixes a linker error observed on nucleo_wb55rg while
preparing an upgrade to Zephyr v3.5.0, caused by an undefined reference to
`z_impl_k_busy_wait`.
Signed-off-by: Maureen Helm <maureen.helm@analog.com>