Convert CONFIG_DIMM_SLOTS_PER_CTLR to Kconfig

This converts the following to Kconfig:
   CONFIG_DIMM_SLOTS_PER_CTLR

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/ddr/fsl/Kconfig b/drivers/ddr/fsl/Kconfig
index 2771670..5925fe9 100644
--- a/drivers/ddr/fsl/Kconfig
+++ b/drivers/ddr/fsl/Kconfig
@@ -53,6 +53,10 @@
 	int "Number of chip selects per controller"
 	default 4
 
+config DIMM_SLOTS_PER_CTLR
+	int "Number of DIMM slots per controller"
+	default 1
+
 config SYS_FSL_DDR_VER
 	int
 	default 50 if SYS_FSL_DDR_VER_50