imx: hab: rework unified rom section for mx7

Rework unified section macro select via Kconfig option
instead of macro definition in mx7_common header file.

Signed-off-by: Adrian Alonso <aalonso@freescale.com>
diff --git a/arch/arm/cpu/armv7/mx7/Kconfig b/arch/arm/cpu/armv7/mx7/Kconfig
index ea19e5c..97d6238 100644
--- a/arch/arm/cpu/armv7/mx7/Kconfig
+++ b/arch/arm/cpu/armv7/mx7/Kconfig
@@ -2,9 +2,11 @@
 
 config MX7
 	bool
+	select ROM_UNIFIED_SECTIONS
 	default y
 
 config MX7D
+	select ROM_UNIFIED_SECTIONS
 	bool
 
 choice