regulators: Add/install config files

Add a `config_files` directory to contain all JSON configuration files
and install all directories/files it contains to
`/usr/share/phosphor-regulators/`.

Tested:
    All directories/files contained are installed
    Installed configs are in /usr/share/phosphor-regulators

Signed-off-by: Matthew Barth <msbarth@us.ibm.com>
Change-Id: I3d67adcd12dd5e05ea333001e9dbb023957551b4
diff --git a/meson.build b/meson.build
index 8740f40..d44ef75 100644
--- a/meson.build
+++ b/meson.build
@@ -4,7 +4,8 @@
     default_options: [
         'warning_level=3',
         'werror=true',
-        'cpp_std=c++17'
+        'cpp_std=c++17',
+        'prefix=/usr'
     ],
     license: 'Apache-2.0',
     version: '1.0',