SPI_STM32_QSPI must be set in buildin as rootfs can be
located on QSPI memory device.

Link: https://lore.kernel.org/r/20191004124025.17394-1-patrice.chotard@st.comSigned-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Olof Johansson <olof@lixom.net>