mtd: st_spi_fsm: begin using spi-nor.h opcodes

Many of the serial_flash_cmds.h opcodes are duplicated with spi-nor.h.
Let's begin to unify them.

Signed-off-by: Brian Norris <computersforpeace@gmail.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
Reviewed-by: Marek Vasut <marex@denx.de>