soc/intel_adsp: bump core count to four for TGPLP cAVS builds

With addition of separate intel_adsp_cavs25_tgph board to
cover 2 core variants, we can now bump the core count to
four cores for intel_adsp_cavs25 (used in Tiger Lake LP PCH).

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>