ramips: fix initramfs image for I-O DATA mt7621 devices

This is additional fix of c998ae7f0e.

The sysupgrade image of I-O DATA MT7621 devices manufactured by MSTC
(MitraStar Technology Corp.) faced to the booting issue. This was caused
by imcomplete extraction of large kernel image by U-Boot, and this issue
is occurred in initramfs image after fixing of sysupgrade image.
So, use lzma-loader for initramfs image to fix the issue.

Signed-off-by: INAGAKI Hiroshi <musashino.open@gmail.com>
Co-developed-by: Yanase Yuki <dev@zpc.sakura.ne.jp>
Signed-off-by: Yanase Yuki <dev@zpc.sakura.ne.jp>
Tested-by: Yanase Yuki <dev@zpc.sakura.ne.jp> [wn-ax2033gr]

target/linux/ramips/image/mt7621.mk

@@ -380,8 +380,8 @@ define Device/iodata_wn-ax1167gr2
   $(Device/iodata_nand)
   UIMAGE_MAGIC := 0x434f4d42
   DEVICE_MODEL := WN-AX1167GR2
-  KERNEL_INITRAMFS := $(KERNEL_DTB) | custom-initramfs-uimage 3.10(XBC.1)b10 | \
-	iodata-mstc-header
+  KERNEL_INITRAMFS := $(KERNEL_DTB) | loader-kernel | lzma | \
+	custom-initramfs-uimage 3.10(XBC.1)b10 | iodata-mstc-header
   DEVICE_PACKAGES := kmod-mt7615e wpad-basic
 endef
 TARGET_DEVICES += iodata_wn-ax1167gr2
@@ -390,8 +390,8 @@ define Device/iodata_wn-ax2033gr
   $(Device/iodata_nand)
   UIMAGE_MAGIC := 0x434f4d42
   DEVICE_MODEL := WN-AX2033GR
-  KERNEL_INITRAMFS := $(KERNEL_DTB) | custom-initramfs-uimage 3.10(VST.1)C10 | \
-	iodata-mstc-header
+  KERNEL_INITRAMFS := $(KERNEL_DTB) | loader-kernel | lzma | \
+	custom-initramfs-uimage 3.10(VST.1)C10 | iodata-mstc-header
   DEVICE_PACKAGES := kmod-mt7603 kmod-mt7615e wpad-basic
 endef
 TARGET_DEVICES += iodata_wn-ax2033gr
@@ -400,8 +400,8 @@ define Device/iodata_wn-dx1167r
   $(Device/iodata_nand)
   UIMAGE_MAGIC := 0x434f4d43
   DEVICE_MODEL := WN-DX1167R
-  KERNEL_INITRAMFS := $(KERNEL_DTB) | custom-initramfs-uimage 3.10(XIK.1)b10 | \
-	iodata-mstc-header
+  KERNEL_INITRAMFS := $(KERNEL_DTB) | loader-kernel | lzma | \
+	custom-initramfs-uimage 3.10(XIK.1)b10 | iodata-mstc-header
   DEVICE_PACKAGES := kmod-mt7615e wpad-basic
 endef
 TARGET_DEVICES += iodata_wn-dx1167r