samples: drivers: CAN: Update to build cleanly for MCP2515 driver

Add alternate conf file for MCP2515 so it builds without warning.
Update documentation.

Signed-off-by: Nick Ward <[email protected]>

Author: nixward

boards/shields/dfrobot_can_bus_v2_0/doc/index.rst

@@ -122,7 +122,8 @@ Zephyr application. For example:
    :tool: all
    :board: nrf52_pca10040
    :shield: dfrobot_can_bus_v2_0
-   :goals: build
+   :conf: prj.mcp2515.conf
+   :goals: build flash
 
 .. _DFRobot Website:
    https://www.dfrobot.com/product-1444.html

samples/drivers/CAN/README.rst

@@ -17,9 +17,35 @@ Building and Running
 In loopback mode, the board receives its own messages. This could be used for
 standalone testing.
 
-The sample can be built and executed on boards supporting CAN.
 The LED output pin is defined in the board's devicetree.
 
+The sample can be built and executed for boards with a SoC that have an
+integrated CAN controller or for boards with a SoC that has been augmented
+with a stand alone CAN controller.
+
+Integrated CAN controller
+=========================
+
+For the NXP TWR-KE18F board:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/drivers/CAN
+   :board: twr_ke18f
+   :goals: build flash
+
+Stand alone CAN controller
+==========================
+
+For the nRF52_PCA10040 board combined with the DFRobot CAN bus V2.0 shield that
+provides the MCP2515 CAN controller:
+
+.. zephyr-app-commands::
+   :zephyr-app: samples/drivers/CAN
+   :board: nrf52_pca10040
+   :shield: dfrobot_can_bus_v2_0
+   :conf: prj.mcp2515.conf
+   :goals: build flash
+
 Sample output
 =============
 

samples/drivers/CAN/prj.mcp2515.conf

@@ -0,0 +1,10 @@
+# Alternate conf file required for building the CAN sample for the
+# MCP2515 stand alone CAN controller
+
+CONFIG_CAN=y
+CONFIG_CAN_INIT_PRIORITY=80
+CONFIG_CAN_MCP2515_MAX_FILTER=5
+
+CONFIG_SHELL=y
+CONFIG_CAN_SHELL=y
+CONFIG_DEVICE_SHELL=y