nvmem: qcom-spmi-sdam: Add support for SPMI SDAM

The SDAM provides scratch register space for the
PMIC clients which can be accessed over the NVMEM
framework. The memory can be used by software to
store information or communicate to/from the PBUS.

Change-Id: Ieb1b8fa296ce7250060d3c036f4ed4ae153b0359
Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>