Add type to adapt mrw version of i2c mux to hb mux type

The MRW xml uses chip-PCA9847 whereas we use i2c_mux_pca9847.  This
changes creates a thin parent class so that we recognize the MRW
type as ours.

Change-Id: I02b74d1f6af24f35e87591c1b1494c02f730e6a0
Reviewed-on: http://rchgit01.rchland.ibm.com/gerrit1/80859
Tested-by: Jenkins Server <pfd-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP Build CI <op-jenkins+hostboot@us.ibm.com>
Tested-by: FSP CI Jenkins <fsp-CI-jenkins+hostboot@us.ibm.com>
Tested-by: Jenkins OP HW <op-hw-jenkins+hostboot@us.ibm.com>
Reviewed-by: William G Hoffa <wghoffa@us.ibm.com>
Reviewed-by: Christian R Geddes <crgeddes@us.ibm.com>
Reviewed-by: Chen Du <duchen@us.ibm.com>
Reviewed-by: Daniel M Crowell <dcrowell@us.ibm.com>

src/usr/targeting/common/xmltohb/target_types.xml

@@ -159,6 +159,13 @@
     <parent>chip-tpm-cectpm</parent>
   </targetType>
 
+  <!-- This special I2C_MUX target adapts the MRW to Hostboot's specific I2C_MUX
+    target. All attributes should be declared against the parent target -->
+  <targetType>
+    <id>chip-PCA9847</id>
+    <parent>i2c_mux_pca9847</parent>
+  </targetType>
+
   <!-- This special UCD target adapts the MRW to Hostboot's specific UCD
       target.  All attributes should be declared against the parent
       target. -->
@@ -1360,8 +1367,7 @@
     </attribute>
   </targetType>
 
-  <!-- This special I2C_MUX target adapts the MRW to Hostboot's specific I2C_MUX
-    target. All attributes should be declared against the parent target -->
+  <!-- Represents a I2C Mux device that is compatible with the PCA9847 spec -->
   <targetType>
     <id>i2c_mux_pca9847</id>
     <parent>chip</parent>