Make PLDM an optional feature for host dump offload

Host dumps are dumps which created and stored in the host
but offloaded through BMC.
With this change if the host dump needs to de downloaded
the transport mechanism also needs to be provided
    --with-host-dump-offload-transport=<transport>
for eg:
    --with-host-dump-offload-transport=pldm
If no options provided the phosphor-dump-manager will be built
with no host dump offload support and an exception will be thrown
if someone tried to call the host dump offload function.

Signed-off-by: Dhruvaraj Subhashchandran <dhruvaraj@in.ibm.com>
Change-Id: I27311427d8ca8b06b9f33ff5f42bdc7ca87fdcd1
diff --git a/offload-extensions/default/default.cpp b/offload-extensions/default/default.cpp
new file mode 100644
index 0000000..6a14fdc
--- /dev/null
+++ b/offload-extensions/default/default.cpp
@@ -0,0 +1,17 @@
+#include <cstdint>
+#include <stdexcept>
+
+namespace phosphor
+{
+namespace dump
+{
+namespace host
+{
+void requestOffload(uint32_t id)
+{
+    throw std::runtime_error("Hostdump offload method not specified");
+}
+
+} // namespace host
+} // namespace dump
+} // namespace phosphor