build: add option KERNEL_DEBUG_INFO_BTF

build: add option KERNEL_DEBUG_INFO_BTF

Generate BTF (BPF Type Format) information from DWARF debug info. This is
embedded in the kernel and exported via sysfs as /sys/kernel/btf/vmlinux.
BTF data enhances kernel portability and introspection for BPF programs.

Selecting this also enables the dwarves host package which provides the
pahole tool used for BTF encoding.

Test using: "bpftool btf dump file /sys/kernel/btf/vmlinux format c"

This needs to depend on KERNEL_DEBUG_INFO_REDUCED not being set,
otherwise we can enable both KERNEL_DEBUG_INFO_BTF and
KERNEL_DEBUG_INFO_REDUCED, which will result in undefined behaviour.

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>
[split DEBUG_INFO_REDUCED into separate commit, add dependency]
Signed-off-by: Stijn Tintel <stijn@linux-ipv6.be>