Add Pican2 support

In order to make Pican 2 work, we :
- add mcp2515.dto to the overlay list
- add a variable to enable it in local.conf
- create a udev rule to mount interface

http://skpang.co.uk/catalog/pican2-canbus-board-for-raspberry-pi-23-p-1475.html

Signed-off-by: Fabien Lahoudere <fabien.lahoudere@collabora.com>

conf/machine/include/rpi-base.inc

@@ -26,6 +26,7 @@ RPI_KERNEL_DEVICETREE_OVERLAYS ?= " \
     overlays/iqaudio-dac.dtbo \
     overlays/iqaudio-dacplus.dtbo \
     overlays/lirc-rpi.dtbo \
+    overlays/mcp2515-can0.dtbo \
     overlays/pi3-disable-bt.dtbo \
     overlays/pi3-miniuart-bt.dtbo \
     overlays/pitft22.dtbo \