mtd: st_spi_fsm: Dynamically setup flash device based on JEDEC ID

Using previously added infrastructure we can now extract a device's JEDEC
ID, compare it to a list of known and supported devices and make assumptions
based on known characteristics of a given chip.

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>