mtd: st_spi_fsm: Move runtime configurable msg sequences into device's struct

Until now the dynamically configurable message sequences for read, write
and enable 32bit addressing have been global. Brian makes a good point
why this should not be the case. If there are ever two FSM's located on
the same platform, we could be potentially introducing a race condition
on "needlessly shared data".

Suggested-by: Brian Norris <computersforpeace@gmail.com>
Acked-by Angus Clark <angus.clark@st.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Brian Norris <computersforpeace@gmail.com>