Include necessary header

Clang complains about not being able to find the printf
implementation without this include

seL4_libs: remove autoconf.h from seL4_libs

this commit removes autoconf.h generation from each lib and
append '#include <<lib_name>/gen_config.h>' after each
'#include <autoconf.h>' since autoconf.h is only the for the
kernel config now. This is a temporarily solution, since we
currently don't have a way to tell which header files each file
is trying to include when it includes 'autoconf.h'

sel4test: trivial: use #pragma once

sel4test: simplify output buffering

- remove BUFFER_OUTPUT, as PRINT_XML implies it
- use config_set where possible
- replace interface with the following:
sel4test_start_printf_buffer: start buffering output
sel4test_end_printf_buffer: dump output and stop buffering
- remove a lot of ifdefs. sel4test is not build for performance
and its
best we compile as much code as possible.
sel4test_start_printf_buffer
does nothing if PRINT_XML is not enabled.

Fix all the whitespace

- remove trailing whitespace
- remove duplicate blank lines
- remove blank lines at end of files

Fix licenses