OpenCL: add add, subtract, multiply prim & rev support for the (scalar, matrix) case

[rok-cesnovar]

Summary

Adds OpenCL support for prim and rev for add, subtract, multiply for cases where one of the arguments is a scalar.

Tests

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Side Effects

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Release notes

Added OpenCL support for prim and rev for add, subtract, multiply for cases where one of the arguments is a scalar.

Checklist

• Math issue Implement matrix_cl overloads for prim & rev functions #1854

• Copyright holder: Rok Češnovar, Uni. of Ljubljana

  The copyright holder is typically you or your assignee, such as a university or company. By submitting this pull request, the copyright holder is agreeing to the license the submitted work under the following licenses:
  - Code: BSD 3-clause (https://opensource.org/licenses/BSD-3-Clause)
  - Documentation: CC-BY 4.0 (https://creativecommons.org/licenses/by/4.0/)

• the basic tests are passing

  • unit tests pass (to run, use: ./runTests.py test/unit)
  • header checks pass, (make test-headers)
  • dependencies checks pass, (make test-math-dependencies)
  • docs build, (make doxygen)
  • code passes the built in C++ standards checks (make cpplint)

• the code is written in idiomatic C++ and changes are documented in the doxygen

• the new changes are tested

[stan-buildbot]

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Name	Old Result	New Result	Ratio	Performance change( 1 - new / old )
gp_pois_regr/gp_pois_regr.stan	3.48	3.38	1.03	2.91% faster
low_dim_corr_gauss/low_dim_corr_gauss.stan	0.02	0.02	1.06	5.86% faster
eight_schools/eight_schools.stan	0.11	0.11	1.01	0.74% faster
gp_regr/gp_regr.stan	0.15	0.15	1.0	0.26% faster
irt_2pl/irt_2pl.stan	5.45	5.45	1.0	0.03% faster
performance.compilation	88.51	85.87	1.03	2.98% faster
low_dim_gauss_mix_collapse/low_dim_gauss_mix_collapse.stan	8.37	8.38	1.0	-0.09% slower
pkpd/one_comp_mm_elim_abs.stan	30.08	30.77	0.98	-2.27% slower
sir/sir.stan	139.09	139.54	1.0	-0.32% slower
gp_regr/gen_gp_data.stan	0.04	0.04	0.98	-2.04% slower
low_dim_gauss_mix/low_dim_gauss_mix.stan	2.93	2.97	0.99	-1.26% slower
pkpd/sim_one_comp_mm_elim_abs.stan	0.41	0.39	1.06	5.31% faster
arK/arK.stan	2.51	2.47	1.02	1.81% faster
arma/arma.stan	0.6	0.59	1.02	2.2% faster
garch/garch.stan	0.61	0.6	1.0	0.39% faster
Mean result: 1.01167964956

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Jenkins Console Log
Blue Ocean
Commit hash: 5117c55

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Machine information

ProductName: Mac OS X ProductVersion: 10.11.6 BuildVersion: 15G22010

CPU:
Intel(R) Xeon(R) CPU E5-1680 v2 @ 3.00GHz

G++:
Configured with: --prefix=/Applications/Xcode.app/Contents/Developer/usr --with-gxx-include-dir=/usr/include/c++/4.2.1
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix

Clang:
Apple LLVM version 7.0.2 (clang-700.1.81)
Target: x86_64-apple-darwin15.6.0
Thread model: posix