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>

dts/bindings/spi/spi-device.yaml

@@ -40,3 +40,21 @@ properties:
     enum:
       - 0
       - 32768
+  spi-cpol:
+    type: boolean
+    description: |
+      SPI clock polarity which indicates the clock idle state.
+      If it is used, the clock idle state is logic high; otherwise, low.
+  spi-cpha:
+    type: boolean
+    description: |
+      SPI clock phase that indicates on which edge data is sampled.
+      If it is used, data is sampled on the second edge; otherwise, on the first edge.
+  spi-hold-cs:
+    type: boolean
+    description: |
+      In some cases, it is necessary for the master to manage SPI chip select
+      under software control, so that multiple spi transactions can be performed
+      without releasing it. A typical use case is variable length SPI packets
+      where the first spi transaction reads the length and the second spi transaction
+      reads length bytes.