support hp as arg for num_layers in dense block

[haifeng-jin]

Which issue(s) does this Pull Request fix?

resolves #000

Details of the Pull Request

[codecov]

Codecov Report

Merging #1419 into master will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##            master     #1419   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files           50        50           
  Lines         2785      2785           
=========================================
  Hits          2785      2785           

Impacted Files	Coverage Δ
autokeras/blocks/basic.py	100.00% <100.00%> (ø)

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