make bootloader_support depend on IDF_TARGET

1. move chip-specific code(e.g. encryption) into IDF_TARGET directory
2. splict app-only code to idf directory which won't be compiled into bootloader

components/bootloader_support/component.mk

@@ -9,6 +9,12 @@ endif
 
 COMPONENT_SRCDIRS := src
 
+ifndef IS_BOOTLOADER_BUILD
+COMPONENT_SRCDIRS += src/idf  # idf sub-directory contains platform agnostic IDF versions
+else
+COMPONENT_SRCDIRS += src/$(IDF_TARGET)  # one sub-dir per chip
+endif
+
 ifndef IS_BOOTLOADER_BUILD
 COMPONENT_OBJEXCLUDE := src/bootloader_init.o
 endif