inga_tool: Extend the Makefile

- The Makefile now contains the full set of default recipes. Without
  them, the compile and link behaviour is implementation-defined
- It now uses pkg-config to check which compiler and linker flags are
  necessary for libftdi, libusb, libudev and popt
- It now uses pkg-config to check which libftdi version is present

However, these changes also make use of GNU Make extensions (namely
%.x targets and conditionals), making the Makefile incompatible with
plain POSIX Make, as does the use of pkg-config.

Also note that inga_tool doesn't yet compile with libftdi1.
inga_tool: Make the indenting consistent

Always use tabs for indenting instead of mixing tabs and spaces.