BugLink: https://bugs.launchpad.net/bugs/1688132

Move common functionality into a separate file in preparation of the
re-use from the ThunderX i2c driver.

Functions are slightly re-ordered but no other changes are included.
Signed-off-by: Jan Glauber <jglauber@cavium.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>
(cherry picked from commit ad83665b)
Signed-off-by: dann frazier <dann.frazier@canonical.com>
Acked-by: Colin King <colin.king@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Signed-off-by: Thadeu Lima de Souza Cascardo <cascardo@canonical.com>