tests: intel_adsp/smoke: wait longer for sched IPI

This lengthens the CPU_IPI_DELAY as some hardware require
a bit more time for IDC to propagate.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>

Author: dcpleung

tests/boards/intel_adsp/smoke/src/smpboot.c

@@ -12,7 +12,7 @@
 #define CPU_START_DELAY 10000
 
 /* IPIs happen  much faster than CPU startup */
-#define CPU_IPI_DELAY 100
+#define CPU_IPI_DELAY 250
 
 BUILD_ASSERT(CONFIG_SMP);
 BUILD_ASSERT(CONFIG_SMP_BOOT_DELAY);