tests/kernel/fpu_sharing/generic: enforce execution on a single CPU

This test relies on one thread interrupting another to exercize the FPU
sharing. On SMP those threads get one CPU each with no sharing of their
FPU making the test rather pointless.

Signed-off-by: Nicolas Pitre <[email protected]>

Author: Nicolas Pitre

tests/kernel/fpu_sharing/generic/prj.conf

@@ -5,3 +5,4 @@ CONFIG_STDOUT_CONSOLE=y
 CONFIG_CBPRINTF_FP_SUPPORT=y
 CONFIG_MAIN_STACK_SIZE=1024
 CONFIG_ZTEST_NEW_API=y
+CONFIG_MP_MAX_NUM_CPUS=1