add specification for netgear .chk files

firmware/netgear_chk.ksy

@@ -0,0 +1,52 @@
+meta:
+  id: netgear_chk
+  title: Netgear chk
+  license: GPL-2.0-or-later
+  endian: be
+  encoding: UTF-8
+doc-ref:
+  - https://lxr.openwrt.org/source/firmware-utils/src/mkchkimg.c
+  - https://github.com/onekey-sec/unblob/blob/5d9fd6d8/unblob/handlers/archive/netgear/chk.py
+seq:
+  - id: header
+    type: header
+  - id: kernel
+    size: header.rest_of_header.len_kernel
+  - id: rootfs
+    size: header.rest_of_header.len_rootfs
+types:
+  header:
+    seq:
+      - id: magic
+        contents: [0x2a, 0x23, 0x24, 0x5e]
+      - id: len_header
+        type: u4
+      - id: rest_of_header
+        type: rest_of_header
+        size: len_header - len_header._sizeof - magic._sizeof
+  rest_of_header:
+    seq:
+      - id: region_code
+        type: u1
+        enum: region_codes
+      - id: reserved
+        size: 7
+      - id: kernel_checksum
+        type: u4
+      - id: rootfs_checksum
+        type: u4
+      - id: len_kernel
+        type: u4
+      - id: len_rootfs
+        type: u4
+      - id: image_checksum
+        type: u4
+      - id: header_checksum
+        type: u4
+      - id: board_id
+        size-eos: true
+        type: str
+enums:
+  region_codes:
+    1: worldwide
+    2: north_america