virt: sev-guest: Explicitly leak pages in unknown state

In the Linux kernel, the following vulnerability has been resolved: virt: sev-guest: Explicitly leak pages in unknown state When set_memory_{encrypted,decrypted}() fail, the user cannot know at which point the function failed, meaning that the pages are left in an unknown state from the point of view of the caller. Since the pages may be left in an unencrypted state, they are not suitable for general use, and cannot be returned safely to the buddy allocator. Avoid the issue by never freeing the pages, and then do the proper accounting by calling snp_leak_pages().