MMIO enhancements to support read and write using different datatype

[mariodruiz]

Support different datatypes for MMIO read and write.

• Merge write functionality in a single method
• MMIO.read arguments word_order and length are deprecated
• MMIO.write detects datatype automatically
• MMIO.read returns the datatype based on the dtype keyword (**kwargs). Eg. mmio.read(offset,dtype=np.float), default is int

Fix #634

[codecov-commenter]

Codecov Report

Merging #1367 (308396a) into image_v2.8 (0cdf6b9) will decrease coverage by 0.04%.
The diff coverage is 95.00%.

@@              Coverage Diff               @@
##           image_v2.8    #1367      +/-   ##
==============================================
- Coverage       46.49%   46.45%   -0.05%     
==============================================
  Files              28       28              
  Lines            4955     4960       +5     
  Branches          971      973       +2     
==============================================
  Hits             2304     2304              
- Misses           2594     2599       +5     
  Partials           57       57              

Impacted Files	Coverage Δ
pynq/overlay.py	33.63% <0.00%> (ø)
pynq/mmio.py	100.00% <100.00%> (ø)
pynq/pl_server/xrt_device.py	29.53% <0.00%> (+0.16%)	⬆️

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[schelleg]

Maintaining MMIO API through next release - closing for now