warp: Fix RAM size runtime detection

Since commit a13d3757f7df ("warp: Use imx_ddr_size() for calculating the
DDR size") warp board no longer boots.

The reason for the breakage is that the warp board is using the DDR
configuration from mx6slevk. A fundamental difference between warp and
mx6slevk is that warp only uses one DDR chip select while mx6slevk uses two.

The imx_ddr() function calculates the RAM size in runtime by reading the
values of registers MDCTL and MDMISC.

So in order to fix this warp boot issue, create a imximage DDR file specific
to warp, where the MDCTL register is configured to only activates a single
chip select.

Reported-by: Breno Lima <breno.lima@nxp.com>
Signed-off-by: Fabio Estevam <fabio.estevam@nxp.com>
Tested-by: Breno Lima <breno.lima@nxp.com>
diff --git a/configs/warp_defconfig b/configs/warp_defconfig
index 389bb7f..786d7e8 100644
--- a/configs/warp_defconfig
+++ b/configs/warp_defconfig
@@ -1,7 +1,7 @@
 CONFIG_ARM=y
 CONFIG_ARCH_MX6=y
 CONFIG_TARGET_WARP=y
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/freescale/mx6slevk/imximage.cfg,MX6SL"
+CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/warp/imximage.cfg,MX6SL"
 CONFIG_BOOTDELAY=3
 CONFIG_HUSH_PARSER=y
 CONFIG_CMD_BOOTZ=y