pragma once and for all

libsel4utils: Move logging macros to libutils

Removed extraneous parentheses

When building with clang the following warnings show up:
warning: equality comparison with extraneous parentheses [-Wparentheses-equality]

Fix licenses

Move sel4_debug.h back into libsel4utils

This patch also renames a header {sel4debug/sel4_debug.h=>sel4utils/strerror.h}.

Additionally, convert some header guards to #pragma once and update
README.md to describe what things should go into libsel4utils and
libsel4debug.

SELFOUR-513

Added sel4_strerror() and some convenience macros for ZF_LOG().

* Moved sel4_strerror and ZF_LOG into seL4_libs, as opposed to util_libs.
* New library function sel4_strerror():
* Does what your gut thinks: prints a stringified version of an seL4 system
error code.
* New macros to make logging cleaner and reduce code size:
* Can be found in sel4_zf_logif.h.
* ZF_LOG?_IF(condition, fmt, ...):
* Prints to log if "condition" is true.
* ZF_LOG?_IFERR(error, fmt, ...):
* Prints to log if error != 0.
* Also prints stringified version of error code.
* Added static index-checking to an array of error-code strings.
* Moved sel4_debug.[ch] from libsel4utils into libsel4debug.