[PATCH v1] spi: designware: add support for bits-per-word DT binding

[Ng, Boon Khai]

Hi Tom,

> I don't see this binding in v7.0-rc1, did I miss it? Thanks.
> 

This binding was not introduce in Linux. This is a per-requisite commit
to support the Agilex Smart NIC 60xx board 
https://www.silicom-usa.com/wp-content/uploads/2024/02/FPGA-SmartNIC-N6010-AgileX-Based.pdf

During the initialization stage, this board require a spi communication 
to configure the chip's PLL and also to check the chip's status.

and it require the specific spi bits-per-word=16 setting.

Can i add the binding at U-Boot?
https://github.com/u-boot/u-boot/blob/master/doc/device-tree-bindings/spi/snps%2Cdw-apb-ssi.txt

Regards
Boon Khai.