kw2xd: Rename CPU kw2x -> kw2xd

NXP calls the family KW2xD in their material.
http://www.nxp.com/products/microcontrollers-and-processors/arm-processors/kinetis-cortex-m-mcus/w-series-wireless-m0-plus-m4:KINETIS_W_SERIES

boards/pba-d-01-kw2x/Makefile.include

@@ -1,5 +1,5 @@
 # define the cpu used by the phyWAVE-KW22 board
-export CPU = kw2x
+export CPU = kw2xd
 export CPU_MODEL = kw21d256
 #export CPU_MODEL = kw21d512
 #export CPU_MODEL = kw22d512

cpu/kw2xd/Makefile.include

@@ -1,4 +1,4 @@
-# define the CPU architecture for the kw2x
+# define the CPU architecture for the kw2xd
 export CPU_ARCH = cortex-m4
 
 # tell the build system that the CPU depends on the Kinetis common files

cpu/kw2xd/cpu.c

@@ -8,7 +8,7 @@
  */
 
 /**
- * @ingroup     cpu_kw2x
+ * @ingroup     cpu_kw2xd
  * @{
  *
  * @file

cpu/kw2xd/include/cpu_conf.h

@@ -8,9 +8,9 @@
  */
 
 /**
- * @defgroup        cpu_kw2x KW2xD SiP
+ * @defgroup        cpu_kw2xd KW2xD SiP
  * @ingroup         cpu
- * @brief           CPU specific implementations for the Freescale KW2xD SiP.
+ * @brief           CPU specific implementations for the NXP/Freescale KW2xD SiP.
  *                  The SiP incorporates a low power 2.4 GHz transceiver and a
  *                  Kinetis Cortex-M4 MCU.
  * @{

cpu/kw2xd/vectors.c

@@ -8,7 +8,7 @@
  */
 
 /**
- * @ingroup     cpu_kw2x
+ * @ingroup     cpu_kw2xd
  * @{
  *
  * @file