ram: k3-ddrss: Introduce top-level CONFIG_K3_DDRSS

Create a new CONFIG_K3_DDRSS option to select the common parts of the
k3-ddrss driver. Also introduce a choice that depends on the top level
option to select CONFIG_K3_J721E_DDRSS for j721e support, and update
corresponding Kconfig as required.

Signed-off-by: Dave Gerlach <d-gerlach@ti.com>
diff --git a/drivers/ram/Makefile b/drivers/ram/Makefile
index 1806a16..5a39611 100644
--- a/drivers/ram/Makefile
+++ b/drivers/ram/Makefile
@@ -15,7 +15,7 @@
 obj-$(CONFIG_K3_AM654_DDRSS) += k3-am654-ddrss.o
 obj-$(CONFIG_ARCH_MEDIATEK) += mediatek/
 obj-$(CONFIG_ARCH_ASPEED) += aspeed/
-obj-$(CONFIG_K3_J721E_DDRSS) += k3-ddrss/
+obj-$(CONFIG_K3_DDRSS) += k3-ddrss/
 
 obj-$(CONFIG_IMXRT_SDRAM) += imxrt_sdram.o