Fixes: quantized_relu & unsigned profiling

[thesps]

Note: bugfixes targeting release branch

quantized_relu

Since this change, we assign the wrong data type to quantized_relu activations. It sets the correct type for quantized_bits, just not quantized_relu. This is what causes the tests flagged in #377 to fail.

Using the example of the hls4ml-tutorial Part3 QKeras model which uses quantized_relu(6) activations, on master branch we assign ap_fixed<6,1>. But appropriate choices would be instead ap_fixed<7,1> (signed) or ap_ufixed<6,0> (unsigned). I've chosen to go for the ap_ufixed case for the fix since it uses fewer bits.

You can see that the types we currently assign to the relu layers are wrong in the profiling:

The model accuracy is:

• 0.743656 QKeras on CPU (reference / target)
• 0.743542 hls4ml on master branch
• 0.743855 hls4ml on this PR (identical if ap_fixed<7,1> was used instead)

The synthesis results slightly prefer the ap_ufixed variation which has one fewer bit than the necessary ap_fixed option.

quantized_relu precision	Accuracy	Latency	II	LUT	FF	DSP	BRAM18
ap_ufixed<6,0>	0.743855	9	1	33706	3037	119	4
ap_fixed<7,1>	0.743855	9	1	37523	3155	119	4

The quantized_relu tests now pass, so they are included again, resolving #377. I added a few more variations as well.

unsigned profiling

In fixing the above, I noticed that we don't display unsigned types correctly in the profiling, so I include the fix for that as well. (Separate commits in case they need to be taken separately).

Before (master):

After (this PR):

[jmduarte]

Thanks @thesps! This looks really good. I just have one minor comment

[jmduarte]

Looks good!