doc: move PVH changelog entry

The feature branch is so old that during rebase it got moved into the
1.8 section. Move it back to the unreleased section.

Signed-off-by: Patrick Roy <[email protected]>

Author: roypat

CHANGELOG.md

@@ -16,6 +16,10 @@ and this project adheres to
   kernels. For older kernels physical counter will still be passed to the guest
   unmodified. See more info
   [here](https://github.com/firecracker-microvm/firecracker/blob/main/docs/prod-host-setup.md#arm-only-vm-physical-counter-behaviour)
+- Added support for PVH boot mode. This is used when an x86 kernel provides the
+  appropriate ELF Note to indicate that PVH boot mode is supported. Linux
+  kernels newer than 5.0 compiled with `CONFIG_PVH=y` set this ELF Note, as do
+  FreeBSD kernels.
 
 ### Changed
 
@@ -192,10 +196,6 @@ and this project adheres to
   [random for clones](docs/snapshotting/random-for-clones.md) documention for
   more info on VMGenID. VMGenID state is part of the snapshot format of
   Firecracker. As a result, Firecracker snapshot version is now 2.0.0.
-- Added support for PVH boot mode.  This is used when an x86 kernel provides
-  the appropriate ELF Note to indicate that PVH boot mode is supported.
-  Linux kernels newer than 5.0 compiled with `CONFIG_PVH=y` set this ELF Note,
-  as do FreeBSD kernels.
 
 ### Changed