atomic_bitmap: add capability to reset bits range

[russell-islam]

Currently, there is no implementation to reset a single bit or bit range for AtomicBitmap struct. This patch adds necessary function to reset a specific bit or a bit range. This use case is needed for Cloud-Hypervisor in managing page cache for Microsoft Hypervisor related to SEV-SNP guest. Rather than implementing a new one , it is helpful to add feature to this struct.

Summary of the PR

Please summarize here why the changes in this PR are needed.

Requirements

Before submitting your PR, please make sure you addressed the following requirements:

• [x] All commits in this PR are signed (with git commit -s), and the commit message has max 60 characters for the summary and max 75 characters for each description line.
• [x] All added/changed functionality has a corresponding unit/integration test.
• [x] All added/changed public-facing functionality has entries in the "Upcoming Release" section of CHANGELOG.md (if no such section exists, please create one).
• [x] Any newly added unsafe code is properly documented.

[russell-islam]

@00xc Could you please take another look into this PR?

[russell-islam]

@alexandruag @bonzini @jiangliu

[russell-islam]

Pinging again: @alexandruag @bonzini @jiangliu