dt-bindings: mfd: stm32f4: Add missing binding definition

This patch adds missing binding definition (backupram, ethernet, otg,
qspi, adc & dsi)

Acked-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Gabriel Fernandez <gabriel.fernandez@st.com>
Signed-off-by: Alexandre TORGUE <alexandre.torgue@st.com>