Enable support for QSPI block on STM32 SoCs.

Link: https://lore.kernel.org/r/20190731072204.32160-1-patrice.chotard@st.comSigned-off-by: Patrice Chotard <patrice.chotard@st.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>