ddr: Migrate DDR_SPD to Kconfig

Move the symbol that controls building some JEDEC SPD support functions
to Kconfig.  This is required on the TI keystone 2 platforms and very
frequently (but not always) used on large number of Freescale/NXP
platforms, so use imply there.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/drivers/ddr/Kconfig b/drivers/ddr/Kconfig
index d4b393d..0b767ac 100644
--- a/drivers/ddr/Kconfig
+++ b/drivers/ddr/Kconfig
@@ -1,2 +1,8 @@
+config DDR_SPD
+	bool "JEDEC Serial Presence Detect (SPD) support"
+	help
+	  For memory controllers that can utilize it, add enable support for
+	  using the JEDEC SDP standard.
+
 source "drivers/ddr/altera/Kconfig"
 source "drivers/ddr/imx/Kconfig"