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"

Also preserve existing behaviour for KERNEL_DEBUG_INFO_REDUCED by adding
it to the "Kernel build options" Kconfig.

Signed-off-by: Tony Ambardar <itugrok@yahoo.com>
Signed-off-by: Felix Fietkau <nbd@nbd.name>