sdcard_image-rpi.bbclass: support for .dtbo files for dtb overlays
sdcard_image-rpi.bbclass: support for .dtbo files for dtb overlays

Kernel 4.4.6+ on RaspberryPi support .dtbo files for overlays, instead of .dtb.
Add support for both extensions for overlays (".dtb" and ".dtbo")

CAUTION: in IMAGE_CMD_rpi-sdimg, 'TMPDIR' is not set, causing 'STAGING_KERNEL_BUILDDIR' to not be expanded, causing get_dts() to not being able to get the kernel version!
To avoid this problem, the kernel version is added in a new variable outside the scope of IMAGE_CMD_rpi-sdimg, and its value passed to get_dts() and split_overlays()!

Signed-off-by: Herve Jourdain <a2a574f9705513524542f7fbeb45f80d5b3c0599@neuf.fr>

schnitzeltony/meta-raspberrypi,schnitzeltony/meta-raspi-light,d21d3q/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,d21d3q/meta-raspberrypi,schnitzeltony/meta-raspi-light,kraj/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,schnitzeltony/meta-raspberrypi,kraj/meta-raspberrypi,leon-anavi/meta-raspberrypi,d21d3q/meta-raspberrypi,agherzan/meta-raspberrypi,toolmmy/meta-raspberrypi,toolmmy/meta-raspberrypi,kraj/meta-raspberrypi,agherzan/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,agherzan/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,schnitzeltony/meta-raspberrypi,agherzan/meta-raspberrypi,agherzan/meta-raspberrypi,leon-anavi/meta-raspberrypi,d21d3q/meta-raspberrypi,LocutusOfBorg/meta-raspberrypi,toolmmy/meta-raspberrypi,toolmmy/meta-raspberrypi