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/configs/mx6qsabrelite_defconfig b/configs/mx6qsabrelite_defconfig
index 27cc261..ba2ea37 100644
--- a/configs/mx6qsabrelite_defconfig
+++ b/configs/mx6qsabrelite_defconfig
@@ -7,6 +7,7 @@
 CONFIG_SYS_MEMTEST_END=0x10010000
 CONFIG_ENV_SIZE=0x2000
 CONFIG_ENV_OFFSET=0xC0000
+CONFIG_IMX_CONFIG="board/boundary/nitrogen6x/nitrogen6q.cfg"
 CONFIG_MX6Q=y
 CONFIG_TARGET_NITROGEN6X=y
 CONFIG_SYS_I2C_MXC_I2C1=y
@@ -17,7 +18,7 @@
 CONFIG_CMD_HDMIDETECT=y
 CONFIG_AHCI=y
 CONFIG_DISTRO_DEFAULTS=y
-CONFIG_SYS_EXTRA_OPTIONS="IMX_CONFIG=board/boundary/nitrogen6x/nitrogen6q.cfg,DDR_MB=1024,SABRELITE"
+CONFIG_SYS_EXTRA_OPTIONS="DDR_MB=1024,SABRELITE"
 CONFIG_BOOTDELAY=3
 # CONFIG_USE_BOOTCOMMAND is not set
 CONFIG_USE_PREBOOT=y