We use hex format for the same information in other parts of the log file.

This brings my original ptp_unpack_EOS_ImageFormat() documentation
up-to-date with new M1/M2 and new 0/1 compression info added with 5Ds,
1DXm2 and R5m2.

It also fixes the problem that led to a double entry of e.g. `RAW` in the
imageformat config output visible in gphoto#1028 and also in the 1DX sample here:
https://github.com/gphoto/libgphoto2/blob/5b7f7c168dd3e86f43b590a7456883e1dec11709/camlibs/ptp2/cameras/canon-eos-1dx.txt#L255-L269

The current `imageformat` with it's table lookup for every RAW+JPEG
combination became cumbersome to maintain and outdated. This leads to
e.g. lost of unsupported JPEG variants for e.g. the 5Ds, R5m2, 1DX.

The used naming also became inconsistent with the addition of the 1DXm2
labels in gphoto@1402f88

This patch adds an (incompatible) new imageformat2 widget as a temporary
test to then hopefully replace the existing imageformat. I expect this new
implementation to fix all "Unknown value" occurrences of all currently
available EOS cameras.

I chose to do away with the verbose and arbitrary labels like
"Smaller Fine JPEG" and instead tried to mimic the strings that are
actually used by the cameras, like 'S2', etc. I added a 'c' for the
higher compression versions, along the lines of 'cRAW'. The 'c' could
also stand for 'coarse' to describe the blocky curve that is used by the
Canons to distinguish between lower and higher Jpeg quality.

Here is some sample output from the 5Ds:
Choice: 5 cM2
Choice: 6 S1
Choice: 7 cS1
Choice: 8 S2
Choice: 9 S3
Choice: 10 RAW + L
Choice: 11 RAW + cL
Choice: 12 RAW + M1
Choice: 13 RAW + cM1