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/configs/ls2080ardb_defconfig b/configs/ls2080ardb_defconfig
index 102d8b3..18bc68d 100644
--- a/configs/ls2080ardb_defconfig
+++ b/configs/ls2080ardb_defconfig
@@ -53,6 +53,7 @@
 CONFIG_SATA_CEVA=y
 CONFIG_FSL_CAAM=y
 CONFIG_DDR_CLK_FREQ=133333333
+CONFIG_DIMM_SLOTS_PER_CTLR=2
 CONFIG_DDR_ECC=y
 CONFIG_ECC_INIT_VIA_DDRCONTROLLER=y
 CONFIG_SYS_I2C_LEGACY=y