regulators: Implement i2c_write_byte action

Implement the i2c_write_byte action in the JSON config file.  See
i2c_write_byte.md for more information about this action.

Signed-off-by: Shawn McCarney <shawnmm@us.ibm.com>
Change-Id: I37fb9b81ee6d9e7fc226787a3242f389b8903714
diff --git a/phosphor-regulators/test/meson.build b/phosphor-regulators/test/meson.build
index 9e2b5bc..f6a351c 100644
--- a/phosphor-regulators/test/meson.build
+++ b/phosphor-regulators/test/meson.build
@@ -17,6 +17,7 @@
     'actions/i2c_compare_bit_action_tests.cpp',
     'actions/i2c_compare_byte_action_tests.cpp',
     'actions/i2c_compare_bytes_action_tests.cpp',
+    'actions/i2c_write_byte_action_tests.cpp',
     'actions/if_action_tests.cpp',
     'actions/not_action_tests.cpp',
     'actions/or_action_tests.cpp',