mtd: st_spi_fsm: Prepare default sequences for read/write/erase

Most chips require a predefined set of FSM message sequences for read,
write and erase operations. This patch provides a way to set them up,
which it will do so if a chip specific initialisation routine isn't
been provided.

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>