hypervisor: maintain a bitmap for SEV-SNP VM on MSHV

Add a bitmap to MshvVM struct for caching the pages
that the VMM got shared access from the guest.

Signed-off-by: Muminul Islam <muislam@microsoft.com>

hypervisor/Cargo.toml

@@ -13,6 +13,7 @@ tdx = []
 
 [dependencies]
 anyhow = "1.0.94"
+arc-swap = "1.7.1"
 byteorder = "1.5.0"
 cfg-if = "1.0.0"
 concat-idents = "1.1.5"
@@ -33,7 +34,11 @@ serde_with = { version = "3.9.0", default-features = false, features = [
 ] }
 thiserror = "1.0.62"
 vfio-ioctls = { workspace = true, default-features = false }
-vm-memory = { workspace = true, features = ["backend-atomic", "backend-mmap"] }
+vm-memory = { workspace = true, features = [
+  "backend-atomic",
+  "backend-bitmap",
+  "backend-mmap",
+] }
 vmm-sys-util = { workspace = true, features = ["with-serde"] }
 
 [target.'cfg(target_arch = "x86_64")'.dependencies.iced-x86]