power-utils: Initially use i2c in updater

Create I2CDevice in updater and invoke read() in doUpdate(), that could
be used in future.
Use mocked I2CInterface in updater's unit test case.

Tested: Manually verify on Witherspoon that the i2c device is opened
        and closed during PSU code update.

Signed-off-by: Lei YU <mine260309@gmail.com>
Change-Id: Ie3d9f0565a2ceb000f489647a58ca967a2ef0c38
diff --git a/meson.build b/meson.build
index d79ba5e..d700891 100644
--- a/meson.build
+++ b/meson.build
@@ -76,6 +76,8 @@
     ],
 )
 
+libpower_inc = include_directories('.')
+
 subdir('phosphor-regulators')
 subdir('power-sequencer')
 subdir('power-supply')