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/meson.build b/phosphor-regulators/meson.build
new file mode 100644
index 0000000..7142616
--- /dev/null
+++ b/phosphor-regulators/meson.build
@@ -0,0 +1,4 @@
+phosphor_regulators_includes = include_directories('src')
+
+subdir('src')
+subdir('test')