include/package.mk: Add support for src-checkout/ folder
drwxr-xr-x - acpi
drwxr-xr-x - asm-generic
drwxr-xr-x - clocksource
drwxr-xr-x - crypto
drwxr-xr-x - drm
drwxr-xr-x - dt-bindings
drwxr-xr-x - keys
drwxr-xr-x - kunit
drwxr-xr-x - kvm
drwxr-xr-x - linux
drwxr-xr-x - math-emu
drwxr-xr-x - media
drwxr-xr-x - misc
drwxr-xr-x - net
drwxr-xr-x - pcmcia
drwxr-xr-x - ras
drwxr-xr-x - rdma
drwxr-xr-x - scsi
drwxr-xr-x - soc
drwxr-xr-x - sound
drwxr-xr-x - target
drwxr-xr-x - trace
drwxr-xr-x - uapi
drwxr-xr-x - vdso
drwxr-xr-x - video
drwxr-xr-x - xen