dt-bindings: iio: bmc150_magn: Document and fix missing compatibles

The driver supports also BMC156B and BMM150B.  Add existing compatibles
marking the BMM150B one as deprecated (due to redundant suffix "_magn"
because the device unlike two others is a magnetometer only).  Introduce
a new, proper compatible for the deprecated one.
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>

Documentation/devicetree/bindings/iio/magnetometer/bmc150_magn.txt

@@ -4,7 +4,11 @@ http://ae-bst.resource.bosch.com/media/products/dokumente/bmc150/BST-BMC150-DS00
 
 Required properties:
 
-  - compatible : should be "bosch,bmc150_magn"
+  - compatible : should be one of:
+                 "bosch,bmc150_magn"
+                 "bosch,bmc156_magn"
+                 "bosch,bmm150"
+                 "bosch,bmm150_magn" (DEPRECATED, use bosch,bmm150)
   - reg : the I2C address of the magnetometer
 
 Optional properties: