keystone2: Move target selection to Kconfig

The config option TARGET_K2x_EVM is set by the k2x defconfigs to pick
a board target, but the header configs also set K2x_EVM. This config
is redundant, remove it and use TARGET_K2x_EVM everywhere in its place.

Signed-off-by: Andrew F. Davis <afd@ti.com>
Reviewed-by: Lokesh Vutla <lokeshvutla@ti.com>
diff --git a/board/ti/ks2_evm/Makefile b/board/ti/ks2_evm/Makefile
index 7ef2d2b..879f8b5 100644
--- a/board/ti/ks2_evm/Makefile
+++ b/board/ti/ks2_evm/Makefile
@@ -6,12 +6,12 @@
 #
 
 obj-y += board.o
-obj-$(CONFIG_K2HK_EVM) += board_k2hk.o
-obj-$(CONFIG_K2HK_EVM) += ddr3_k2hk.o
-obj-$(CONFIG_K2E_EVM) += board_k2e.o
-obj-$(CONFIG_K2E_EVM) += ddr3_k2e.o
-obj-$(CONFIG_K2L_EVM) += board_k2l.o
-obj-$(CONFIG_K2L_EVM) += ddr3_k2l.o
-obj-$(CONFIG_K2L_EVM) += ddr3_cfg.o
-obj-$(CONFIG_K2G_EVM) += board_k2g.o
-obj-$(CONFIG_K2G_EVM) += ddr3_k2g.o
+obj-$(CONFIG_TARGET_K2HK_EVM) += board_k2hk.o
+obj-$(CONFIG_TARGET_K2HK_EVM) += ddr3_k2hk.o
+obj-$(CONFIG_TARGET_K2E_EVM) += board_k2e.o
+obj-$(CONFIG_TARGET_K2E_EVM) += ddr3_k2e.o
+obj-$(CONFIG_TARGET_K2L_EVM) += board_k2l.o
+obj-$(CONFIG_TARGET_K2L_EVM) += ddr3_k2l.o
+obj-$(CONFIG_TARGET_K2L_EVM) += ddr3_cfg.o
+obj-$(CONFIG_TARGET_K2G_EVM) += board_k2g.o
+obj-$(CONFIG_TARGET_K2G_EVM) += ddr3_k2g.o