Create stubs for regulator Device, Rail, and Rule

Create stub versions of the Device, Rail, and Rule classes for the
phosphor-regulators application.  Having a stub version of these classes
is a pre-requisite for implementing the action framework.

Also updated the top level meson.build file to build the
phosphor-regulators directory.  Created new meson.build files for
several phosphor-regulators sub-directories.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I50b018db744191acd1e473652019906a8506745f
diff --git a/phosphor-regulators/test/meson.build b/phosphor-regulators/test/meson.build
new file mode 100644
index 0000000..0e32ad7
--- /dev/null
+++ b/phosphor-regulators/test/meson.build
@@ -0,0 +1,15 @@
+test('phosphor-regulators-tests',
+     executable('phosphor-regulators-tests',
+                'device_tests.cpp',
+                'rail_tests.cpp',
+                'rule_tests.cpp',
+                dependencies: [
+                    gmock,
+                    gtest,
+                ],
+                implicit_include_directories: false,
+                include_directories: phosphor_regulators_includes,
+     )
+)
+
+# subdir('actions')