binfmt: finetune selection

m68k one memory region generates broken code with SIGILL exceptions.
bfin is only one memory region only.

target/config/Config.in.binfmt

@@ -33,11 +33,13 @@ default ADK_TARGET_BINFMT_FLAT_ONE
 
 config ADK_TARGET_BINFMT_FLAT_ONE
 	bool "One memory region"
+	depends on ADK_TARGET_ARCH_BFIN
 	help
 	  All segments are linked into one memory region.
 
 config ADK_TARGET_BINFMT_FLAT_SEP_DATA
 	bool "Separate data and code region"
+	depends on ADK_TARGET_ARCH_M68K
 	help
 	  Allow for the data and text segments to be separated and placed in
 	  different regions of memory.