CONFIG_DEBUG_INFO_BTF significantly increases compile time for the
kernel. E.g. when changing a single C file compile time for a new bzImage
is increased by ~50% if BTF debug info is generated.

Therefore remove CONFIG_DEBUG_INFO_BTF from all defconfigs and introduce a
btf.config addon config file. Quickly enabling CONFIG_DEBUG_INFO_BTF into
the current kernel config can be done by simply invoking

make btf.config
Reviewed-by: Alexander Gordeev <agordeev@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Alexander Gordeev <agordeev@linux.ibm.com>