feat: added gm8126 SPI image header signature

Author: jstucke

mime/firmware_containers

@@ -934,3 +934,11 @@
 >0x46  ubequad x   md5: %016llx,
 >0x78   ubelong x   header sum: 0x%x,
 >0x7c   ubelong x   magic: 0x%x
+
+# GM8126 SPI Flash Image Header
+0   string  \x80\x5a\x47\x4d    GM8126 SPI Flash Image Header,
+!:mime firmware/gm8126
+# the Image CRC is usually zero
+>0x04  ubelong x   Image CRC: 0x%x,
+>0x08  ubelong x   Image Size: %d,
+>0x10   string  x   Image Name: %s