test: msgq: remove number of cpu restriction

Remove CONFIG_MP_NUM_CPU=1 from test cases of msgq.
For CONFIG_MP_NUM_CPU > 1, start a thread with K_NO_WAIT to get
message from message queue will run immediately on another cpu and
cause message peek failure if there is no message in queue, so put
messages in msgq before start that thread.

Signed-off-by: Meng xianglin <xianglinx.meng@intel.com>