imx: Finish migration of IMX_CONFIG to Kconfig

- Provide a default Kconfig value of the default script
- Largely continue to define this via the board Kconfig file
- For the boards that select a script based on defconfig rather than
  TARGET, keep this within the defconfig.

Signed-off-by: Tom Rini <trini@konsulko.com>
diff --git a/board/phytec/pcm052/Kconfig b/board/phytec/pcm052/Kconfig
index 4fde21c..23f2565 100644
--- a/board/phytec/pcm052/Kconfig
+++ b/board/phytec/pcm052/Kconfig
@@ -13,6 +13,9 @@
 	int
 	default 256
 
+config IMX_CONFIG
+	default "board/phytec/pcm052/imximage.cfg"
+
 endif
 
 if TARGET_BK4R1
@@ -30,4 +33,7 @@
 	int
 	default 512
 
+config IMX_CONFIG
+	default "board/phytec/pcm052/imximage.cfg"
+
 endif