Add a Kconfig option to control whether full kmem_cache_free() and
kmem_cache_destroy() implementations are provided in lib/linux_compat.c
Most boards do not need these functions, so they can use simple inline
stubs in slab.h. Subsystems like ext4 that require proper cache
management can select CONFIG_LIB_KMEM_CACHE.
Co-developed-by: Claude <noreply@anthropic.com>
Signed-off-by: Simon Glass <simon.glass@canonical.com>
