regulators: Build IDMap for system

The IDMap class is used to map string IDs to the corresponding C++
Device, Rail, and Rule objects.

The IDMap class is complete and tested, but it was not previously being
populated except in testcases.

Add new methods to the System, Chassis, and Device classes to populate
the IDMap with all the ID -> object mappings in the system.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I80f39b663b011ca643c91f7281ff50c956631331
diff --git a/phosphor-regulators/src/meson.build b/phosphor-regulators/src/meson.build
index 3caa543..aa8921c 100644
--- a/phosphor-regulators/src/meson.build
+++ b/phosphor-regulators/src/meson.build
@@ -4,9 +4,12 @@
 )
 
 phosphor_regulators_library_source_files = [
+    'chassis.cpp',
     'config_file_parser.cpp',
+    'device.cpp',
     'id_map.cpp',
     'pmbus_utils.cpp',
+    'system.cpp',
 
     'actions/if_action.cpp',
     'actions/i2c_compare_bit_action.cpp',