[kernel] Move the logger from kutil into kernel

Part one of a series of code moves. The kutil library is not very
useful, as most of its code is kernel-specific. This was originally for
testing purposes, but that can be achieved in other ways with the
current build system. I find this mostly creates a strange division in
the kernel code.

Instead, I'm going to move everything kernel-specific to actually be in
the kernel, and replace kutil with just 'util' for generic utility code
I want to share.

This commit:

- Moves the logger into the kernel.
- Updates the 'printf' library used from mpaland/printf to
  eyalroz/printf and moved it into the kernel, as it's only used by the
  logger in kutil.
- Removes some other unused kutil headers from some files, to help
  future code rearrangement.

Note that the (now redundant-seeming) log.cpp/h in kernel is currently
still there - these files are more about log output than the logging
system, and will get replaced once I add user-space log output.

configs/kernel-debug.yaml

@@ -24,6 +24,8 @@ variables:
     "-D__JSIX__",
     "-U__linux",
     "-U__linux__",
+    "-DPRINTF_ALIAS_STANDARD_FUNCTION_NAMES=1",
+    "-DPRINTF_INCLUDE_CONFIG_H=1",
 
     "-isystem${source_root}/sysroot/include",
     "-isystem${source_root}/src/libraries/libc/include",