fw-update: Break circular dependency

```
In file included from ../pldmd/pldmd.cpp:2:
In file included from ../common/flight_recorder.hpp:3:
In file included from ../common/utils.hpp:15:
In file included from ../subprojects/nlohmann_json/single_include/nlohmann/json.hpp:29:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/memory:78:
/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/bits/unique_ptr.h:91:16: error: invalid application of 'sizeof' to an incomplete type 'pldm::fw_update::Activation'
   91 |         static_assert(sizeof(_Tp)>0,
      |                       ^~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/bits/unique_ptr.h:398:4: note: in instantiation of member function 'std::default_delete<pldm::fw_update::Activation>::opera
tor()' requested here
  398 |           get_deleter()(std::move(__ptr));
      |           ^
../fw-update/update_manager.hpp:46:14: note: in instantiation of member function 'std::unique_ptr<pldm::fw_update::Activation>::~unique_ptr' requested here
   46 |     explicit UpdateManager(
      |              ^
../fw-update/update_manager.hpp:33:7: note: forward declaration of 'pldm::fw_update::Activation'
   33 | class Activation;
      |       ^
In file included from ../pldmd/pldmd.cpp:2:
In file included from ../common/flight_recorder.hpp:3:
In file included from ../common/utils.hpp:15:
In file included from ../subprojects/nlohmann_json/single_include/nlohmann/json.hpp:29:
In file included from /usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/memory:78:
/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/bits/unique_ptr.h:91:16: error: invalid application of 'sizeof' to an incomplete type 'pldm::fw_update::ActivationProgress'
   91 |         static_assert(sizeof(_Tp)>0,
      |                       ^~~~~~~~~~~
/usr/bin/../lib/gcc/x86_64-linux-gnu/14/../../../../include/c++/14/bits/unique_ptr.h:398:4: note: in instantiation of member function 'std::default_delete<pldm::fw_update::ActivationProgress
>::operator()' requested here
  398 |           get_deleter()(std::move(__ptr));
      |           ^
../fw-update/update_manager.hpp:46:14: note: in instantiation of member function 'std::unique_ptr<pldm::fw_update::ActivationProgress>::~unique_ptr' requested here
   46 |     explicit UpdateManager(
      |              ^
../fw-update/update_manager.hpp:34:7: note: forward declaration of 'pldm::fw_update::ActivationProgress'
   34 | class ActivationProgress;
      |       ^
```

Change-Id: I2820cbe134d1f37a43e6a5056eed87dde6e63b08
Signed-off-by: Andrew Jeffery <andrew@codeconstruct.com.au>
diff --git a/meson.build b/meson.build
index 100c0f9..bfbf63e 100644
--- a/meson.build
+++ b/meson.build
@@ -164,6 +164,7 @@
   'pldmd',
   'pldmd/pldmd.cpp',
   'pldmd/dbus_impl_pdr.cpp',
+  'fw-update/activation.cpp',
   'fw-update/inventory_manager.cpp',
   'fw-update/package_parser.cpp',
   'fw-update/device_updater.cpp',