dts: bindings: spi: add support to set CPOL, CPHA, and HOLD_CS in dts file

Add support to set SPI clock polarity (CPOL), clock phase (CPHA), and
hold-on-cs in a dts file to get rid of using related macros in spi.c driver
since each board may work on a different SPI mode rather than the default
one (based on CPOL and CPHA).

Signed-off-by: Ali Hozhabri <ali.hozhabri@st.com>