mmc: Update and remove functions for the kernel and rootfs

Add support for update and remove of eMMC images.

The code update tarball contains an image-kernel and image-rofs
files. These can be flashed directly to the eMMC partitions since
they're filesystem files compressed with zstd:

https://gerrit.openbmc-project.xyz/c/openbmc/meta-phosphor/+/30781
https://gerrit.openbmc-project.xyz/c/openbmc/meta-phosphor/+/34334

The image-rofs contains the BMC rootfs files, and the image-kernel
contains the fitImage file which is loaded by U-Boot.

Tested: Verified the non-running rofs and kernel partitions were updated.

Change-Id: Ic983dec1df389d56f11f12dc2e82589d1a2b9dcc
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/mmc/item_updater_helper.cpp b/mmc/item_updater_helper.cpp
index 8ef5749..0eb910e 100644
--- a/mmc/item_updater_helper.cpp
+++ b/mmc/item_updater_helper.cpp
@@ -1,3 +1,5 @@
+#include "config.h"
+
 #include "item_updater_helper.hpp"
 
 namespace phosphor
@@ -27,9 +29,13 @@
     // Empty
 }
 
-void Helper::removeVersion(const std::string& /* versionId */)
+void Helper::removeVersion(const std::string& versionId)
 {
-    // Empty
+    auto method = bus.new_method_call(SYSTEMD_BUSNAME, SYSTEMD_PATH,
+                                      SYSTEMD_INTERFACE, "StartUnit");
+    auto serviceFile = "obmc-flash-mmc-remove@" + versionId + ".service";
+    method.append(serviceFile, "replace");
+    bus.call_noreply(method);
 }
 
 void Helper::updateUbootVersionId(const std::string& /* versionId */)