Clarify what licences apply where

This doesn't change any license, just clarifies what's licensed under
LGPL and what's under GPL.
testsuite: add tests for array implementation
Do not export array of kmod extensions

The only user outside of libkmod-util is depmod, which really only needs
to get the string for the extension of uncompressed modules. It doesn't
need to access the array itself.
Do not rely on prio_to_str() being always inline

This function was declared as always-inline so there was not really a
problem in returning prioname, that could possibly point to the local
buf[] variable.

However static analysis tools are often confused about this and being
always-inline was just a workaround to make it work.

So, let's move the buffer to the caller. We have only 2 callers so it
doesn't matter much. This always reduce the size of log.o, since now the
function is not inlined anymore. Below is the size for "-g -O2" with
gcc:

before:
   text    data     bss     dec     hex filename
   1325       4       1    1330     532 tools/log.o

after:
   text    data     bss     dec     hex filename
   1171       4       1    1176     498 tools/log.o
Move alias_normalize() to shared
depmod: use alias_normalize() from shared

Remove underscores2() function which is essentially the same as
alias_normalize() and the latter, which is now in shared/.
Move remaining functions from libkmod-util to shared
build-sys: rename libkmod-util convenience library

Now that all source code from libkmod-util has been moved to shared/
directory, rename also the convenience library to libshared.