Create regulators IfAction class

Create the IfAction class that implements the "if" action in the JSON
config file.

See phosphor-regulators/docs/config_file/if.md for more information on
the "if" action.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I16d5ba7bb88b5baa8a5085168a8bd2dc75449e9b
diff --git a/phosphor-regulators/src/meson.build b/phosphor-regulators/src/meson.build
index 76551ae..e93d65f 100644
--- a/phosphor-regulators/src/meson.build
+++ b/phosphor-regulators/src/meson.build
@@ -4,7 +4,9 @@
 )
 
 phosphor_regulators_source_files = [
-    'id_map.cpp'
+    'id_map.cpp',
+
+    'actions/if_action.cpp'
 ]
 
 phosphor_regulators_library = static_library(