dual-image: Fix the install of obmc-flash-bmc-alt@.service

The obmc-flash-bmc-alt@.service was installed without
bmc-static-dual-image config enabled, this causes the incorrect install
of the service when the config is not enabled.

Fix this by install the service only when bmc-static-dual-image is
enabled.

Signed-off-by: Lei YU <yulei.sh@bytedance.com>
Change-Id: I4ae2c0038999bd997ec07ca8b800597c87de00cc
diff --git a/meson.build b/meson.build
index 24abdc1..201f0b9 100644
--- a/meson.build
+++ b/meson.build
@@ -188,9 +188,6 @@
         'static/flash.cpp',
         'static/item_updater_helper.cpp'
     )
-    unit_files += [
-        'static/obmc-flash-bmc-alt@.service.in',
-    ]
 elif get_option('bmc-layout').contains('ubi')
     image_updater_sources += files(
         'ubi/flash.cpp',
@@ -228,6 +225,7 @@
 
 if get_option('bmc-static-dual-image').enabled()
     unit_files += [
+        'static/obmc-flash-bmc-alt@.service.in',
         'static/obmc-flash-bmc-static-mount-alt.service.in',
         'static/obmc-flash-bmc-prepare-for-sync.service.in',
     ]