esp32/Makefile: Put all IDF compenents in .a libs to use IDF ld script.

When the ESP IDF builds a project it puts all separate components into
separate .a library archives.  And then the esp32.common.ld linker script
references these .a libraries by explicit name to put certain object files
in iRAM.

This patch does a similar thing for the custom build system used here,
putting all IDF .o's into their respective .a.  So a custom linker script
is no longer needed.