Add Microsoft Azure Pipelines configuration

Add Microsoft Azure Pipelines configuration

Microsoft Azure Pipelines [1] provides unlimited CI/CD minutes and
10 parallel jobs to every open source project for free.

This adds a configuration file for Azure Pipelines to utilize the
free Windows VM hosted by Microsoft to ensure no build broken in
building U-Boot host tools for Windows.

[1] https://azure.microsoft.com/en-us/blog/announcing-azure-pipelines-with-unlimited-ci-cd-minutes-for-open-source/

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>