nvmem: add QTI SDAM driver

QTI SDAM driver allows PMIC peripherals to access the shared memory
that is available on QTI PMICs.

Use subsys_initcall as PMIC SDAM NV memory is accessed by multiple PMIC
drivers (charger, fuel gauge) to store/restore data across reboots
required during their initialization.

Signed-off-by: Anirudh Ghayal <aghayal@codeaurora.org>
Signed-off-by: Shyam Kumar Thella <sthella@codeaurora.org>
Signed-off-by: Srinivas Kandagatla <srinivas.kandagatla@linaro.org>
Link: https://lore.kernel.org/r/20200116161100.30637-4-srinivas.kandagatla@linaro.org
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>