[media] em28xx: add basic support for eeproms with 16 bit address width

Newer devices (em2874, em2884, em28174, em25xx, em27[6,7,8]x) use eeproms with
16 bit instead of 8 bit address width.
The used eeprom type depends on the chip type, which makes sure eeproms can't
be damaged.
This patch adds basic support for 16 bit eeproms only, which includes
- reading the content
- calculating the eeprom hash
- displaying the content
The eeprom content uses a different format, for which support will be added with
subsequent patches.
Tested with the "Hauppauge HVR-930C" and the "Speedlink VAD Laplace webcam"
(with additional experimental patches).

Signed-off-by: Frank Schäfer <fschaefer.oss@googlemail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>