add EVA kernel image signatures

[grische]

These files follow the following structure:
https://gist.github.com/grische/a84ba742743a8f046a8f81e0b1ffc3eb

A dual-kernel example file can be obtained by downloading a firmware file from https://download.avm.de/fritzbox/fritzbox-7590-ax/other/fritz.os/ and extracting the kernel image from the tar container.

-------------------------------------------------------------------------------------------------------------------
DECIMAL                            HEXADECIMAL                        DESCRIPTION
-------------------------------------------------------------------------------------------------------------------
0                                  0x0                                Fritz!Box EVA kernel image, dual-kernel,
                                                                      primary load: 0x80500000, entry: 0x80C00000,
                                                                      compressed: 59 bytes, uncompressed: 320
                                                                      bytes, secondary load: 0x8DFF0000, entry:
                                                                      0x8DFF1000, compressed: 59 bytes,
                                                                      uncompressed: 320 bytes, file signature CRC:
                                                                      0xE64A587B
-------------------------------------------------------------------------------------------------------------------

[grische]

Was merged in the new fork binwalk-ng#26