treewide: add sysupgrade comment for early DSA-adopters

Add a specific comment for early DSA-adopters that they can keep
their config when prompted due to compat-version increase.

This is a temporary solution, the patch should be simply reverted
before any release.

Signed-off-by: Adrian Schmutzler <[email protected]>

target/linux/kirkwood/image/Makefile

@@ -12,7 +12,8 @@ KERNEL_LOADADDR:=0x8000
 
 define Device/dsa-migration
   DEVICE_COMPAT_VERSION := 1.1
-  DEVICE_COMPAT_MESSAGE := Config cannot be migrated from swconfig to DSA
+  DEVICE_COMPAT_MESSAGE := Config cannot be migrated from swconfig to DSA \
+	(early adopters with DSA already set up may just force-flash keeping existing config)
 endef
 
 define Device/Default

target/linux/mvebu/image/cortexa9.mk

@@ -8,7 +8,8 @@
 
 define Device/dsa-migration
   DEVICE_COMPAT_VERSION := 1.1
-  DEVICE_COMPAT_MESSAGE := Config cannot be migrated from swconfig to DSA
+  DEVICE_COMPAT_MESSAGE := Config cannot be migrated from swconfig to DSA \
+	(early adopters with DSA already set up may just force-flash keeping existing config)
 endef
 
 define Device/buffalo_ls421de

target/linux/ramips/image/mt7621.mk

@@ -107,7 +107,8 @@ endef
 
 define Device/dsa-migration
   DEVICE_COMPAT_VERSION := 1.1
-  DEVICE_COMPAT_MESSAGE := Config cannot be migrated from swconfig to DSA
+  DEVICE_COMPAT_MESSAGE := Config cannot be migrated from swconfig to DSA \
+	(early adopters with DSA already set up may just force-flash keeping existing config)
 endef
 
 define Device/adslr_g7