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/siemens/capricorn/Kconfig b/board/siemens/capricorn/Kconfig
index 21c3ef9..c5a28ff 100644
--- a/board/siemens/capricorn/Kconfig
+++ b/board/siemens/capricorn/Kconfig
@@ -9,6 +9,8 @@
 config SYS_CONFIG_NAME
 	default "giedi"
 
+config IMX_CONFIG
+	default "board/siemens/capricorn/imximage.cfg"
 endif
 
 if TARGET_DENEB
@@ -22,4 +24,7 @@
 config SYS_CONFIG_NAME
 	default "deneb"
 
+config IMX_CONFIG
+	default "board/siemens/capricorn/imximage.cfg"
+
 endif