siemens: cosmetic: remove unused and rename defines

For dxr2 board DXR2_IOCTRL_VAL is set by data in EEPROM. In pxm2
board it does not make sense to have dxr2 as prefix. Replace it with
more meaningful DDR prefix.

Signed-off-by: Samuel Egli <samuel.egli@siemens.com>
Cc: Pascal Bach <pascal.bach@siemens.com>
Cc: Roger Meier <r.meier@siemens.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Wolfgang Denk <wd@denx.de>
diff --git a/board/siemens/pxm2/board.c b/board/siemens/pxm2/board.c
index 98083d5..64e69dc 100644
--- a/board/siemens/pxm2/board.c
+++ b/board/siemens/pxm2/board.c
@@ -70,11 +70,11 @@
 };
 
 const struct ctrl_ioregs ioregs = {
-	.cm0ioctl		= DXR2_IOCTRL_VAL,
-	.cm1ioctl		= DXR2_IOCTRL_VAL,
-	.cm2ioctl		= DXR2_IOCTRL_VAL,
-	.dt0ioctl		= DXR2_IOCTRL_VAL,
-	.dt1ioctl		= DXR2_IOCTRL_VAL,
+	.cm0ioctl		= DDR_IOCTRL_VAL,
+	.cm1ioctl		= DDR_IOCTRL_VAL,
+	.cm2ioctl		= DDR_IOCTRL_VAL,
+	.dt0ioctl		= DDR_IOCTRL_VAL,
+	.dt1ioctl		= DDR_IOCTRL_VAL,
 };
 
 	config_ddr(DDR_PLL_FREQ, &ioregs, &pxm2_ddr3_data,