UPSTREAM: mfd: sc27xx: Add USB charger type detection support

The Spreadtrum SC27XX series PMICs supply the USB charger type detection
function, and related registers are located on the PMIC global registers
region, thus we implement and export this function in the MFD driver for
users to get the USB charger type.

bug: 153500755
Change-Id: I18ef05b27c61ad915c86ddf26420fe92c8516552
Signed-off-by: Baolin Wang <baolin.wang7@gmail.com>
Signed-off-by: Lee Jones <lee.jones@linaro.org>
(cherry picked from commit 2a7e7274f3d43d2a072cab25c0035dc994903bb9)