mmc: Move process host firmware to own service

The process-host-firmware subcommand waits for the Entity Manager
interface to appear in D-Bus. It's currently run from the mmc-init
script. But if a system does not support Entity Manager, then the init
service never exits, blocking its dependencies like PLDM from starting.

Move the process-host-firmware to its own service file so that if needs
to wait forever, it doesn't interfere with other processes. Need to
start it after the mmc-init so that all the directories are setup before
the symlinks are created.

Tested: Verified on tacoma that the service remains running and PLDM
starts successfully. Verified on rainier that the symlinks are created.

Change-Id: Ia746362e5ff688b972e9b92e9d78f3f5b3623a99
Signed-off-by: Adriana Kobylak <anoo@us.ibm.com>
diff --git a/meson.build b/meson.build
index 1aca29a..1b654b2 100644
--- a/meson.build
+++ b/meson.build
@@ -124,6 +124,7 @@
     extra_unit_files += [
         'mmc/obmc-flash-bios-init.service',
         'mmc/obmc-flash-bios-patch.service',
+        'mmc/openpower-process-host-firmware.service',
     ]
 endif