boards: arm: stm32l4s5 disco kit with octospi on board

Activates the NOR octoflash MX25r6435f present on the disco kit
b_l4s5i_iot02a from STMicroelectronics.
The connection is made through the OSPIM peripheral for the
octospi1 pins.
QUAD spi mode is selected but SPI or DUAL are also supported.
SPI Max freq is given by the datasheet
and is compatible with Voltage Range 2.
DMAMUX is used for ospi transfer on request 40.

Signed-off-by: Francois Ramu <francois.ramu@st.com>