meson: do not use split() in file lists

meson: do not use split() in file lists

The approach to use '''…'''.split() instead of a list of strings was initially
used when converting from automake because it allowed identical blocks of lines
to be used for both, making the conversion easier.

But over the years we have been using normal lists more and more, especially
when there were just a few filenames listed. This converts the rest.

No functional change.