dt-bindings: Add vendor prefix for Shiratech Solutions

This commit adds devicetree vendor prefix for Shiratech solutions,
a SOM/embedded board manufacturing company.

https://www.shiratech-solutions.com/



Signed-off-by: Manivannan Sadhasivam <mani@kernel.org>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Alexandre Torgue <alexandre.torgue@st.com>