ST: - the line is valid for SPL and TPL images
+S: - the line is valid for Normal and SPL images
+T: - the line is valid for Normal and TPL images
- +ST: - the line is valid for Normal, SPL and SPL images
+ +ST: - the line is valid for Normal, SPL and TPL images
So, if neither CONFIG_SPL nor CONFIG_TPL is defined, the defconfig file
has no "<condition>:" part and therefore has the same form as in Linux.