spa: support: do not include C source file

Previously, `log-patterns.c` was included in two other source files
(`journal.c` and `logger.c`). It was also specified in the sources
list for the libspa-support library, which resulted in the unnecessary
independent compilation of the file, generating "defined but not used"
warnings.

Extract the function definitions into `log-patterns.h` and
use that in `journal.c` and `logger.c`, and remove the inclusion
of `log-patterns.c` from both.