spmi: add glink debug spmi controller driver

Add an SPMI controller driver for the Glink PMIC register
dumping debug interface.  This can be used to read and write
PMIC registers controlled by the charging firmware running
on a remote processor (e.g. DSP).

Change-Id: I10d0c345e35613c708eea0d2fbb9fd0e03ecf2b5
Signed-off-by: David Collins <collinsd@codeaurora.org>