Add support for Alpha 7RII aka ILCE-7RM2 raw format

[lucalista]

When opening with Image.open a RAW image file produced by a SONY Alpha 7RII aka ILCE-7RM2, an exception is risen:

cannot identify image file '/Users/xxx/Pictures/SONY-RAW/RAW_SONY_ILCE-7RM2.ARW'

A sample image can be downloaded from the following URL:

http://www.rawsamples.ch/raws/sony/RAW_SONY_ILCE-7RM2.ARW

I would appreciate if the support could be extended to this RAW format as well.

[radarhere]

The file you have provided is very similar to the one from #3124. Pillow tries to open it as a TIFF, but can't find the width and height, and doesn't have an OPEN_INFO entry for (b'II', 6, (1,), 1, (1, 1, 1), ()).

Do you mind if this issue is subsumed into a general issue we have for Raw formats (#6482), or would you like it to be kept open separately?