ramips: only limit lzma dictionary size on mt7621

The changed dictionary size leads to a different LZMA header which breaks
sysupgrade image magic checkibng on at least some RT288x boards.

Since the commit message only mentions testing on MT7621 and since the
change appears to break at least one other ramips subtarget, do not take
any chances and restrict the size limitation to only MT7621.

Fixes FS#1797
Fixes 09b6755946 ("ramips: limit dictionary size for lzma compression")
Signed-off-by: Jo-Philipp Wich <jo@mein.io>

target/linux/ramips/image/Makefile

@@ -31,7 +31,7 @@ loadaddr-$(CONFIG_TARGET_ramips_mt7621) := 0x80001000
 
 KERNEL_LOADADDR := $(loadaddr-y)
 
-KERNEL_DTB = kernel-bin | patch-dtb | lzma -d21
+KERNEL_DTB = kernel-bin | patch-dtb | lzma
 define Device/Default
   PROFILES = Default $$(DTS)
   KERNEL_DEPENDS = $$(wildcard ../dts/$$(DTS).dts)

target/linux/ramips/image/mt7621.mk

@@ -2,6 +2,7 @@
 # MT7621 Profiles
 #
 
+KERNEL_DTB += -d21
 DEVICE_VARS += TPLINK_BOARD_ID TPLINK_HEADER_VERSION TPLINK_HWID TPLINK_HWREV
 
 define Build/elecom-gst-factory