staging: wilc1000: move struct Message and WILC_MsgQueueHandle

This patch moves struct Message and WILC_MsgQueueHandle from
wilc_platform.h to wilc_msgqueue.h because those two structures are used
only at wilc_msgqueue.c so that it is good to be defined at
wilc_msgqueue.h

Signed-off-by: Chaehyun Lim <chaehyun.lim@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>