scripts: Makefile.spl: Enable memory drivers to be built for SPL

Introduce CONFIG_SPL_MEMORY to allow Memory drivers to
be built for SPL.

Signed-off-by: Roger Quadros <rogerq@kernel.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/common/spl/Kconfig b/common/spl/Kconfig
index b1b9e09..b738c74 100644
--- a/common/spl/Kconfig
+++ b/common/spl/Kconfig
@@ -796,6 +796,13 @@
 	  this option to build the drivers in drivers/mailbox as part of
 	  SPL build.
 
+config SPL_MEMORY
+	bool "Support Memory controller drivers"
+	help
+	  Enable support for Memory Controller drivers within SPL.
+	  These devices provide Memory bus interface to various devices like
+	  SRAM, Ethernet adapters, FPGAs, etc.
+
 config SPL_MMC
 	bool "Support MMC"
 	depends on MMC