drivers: regulator: cpr-regulator: Add support for the new scm_call2 API

The scm library has added support for a new secure world
interface that is more aligned to the ARMv8 SMC calling
convention. Use the new API while maintaining backward
compatibility.

Change-Id: I9e93d2120d91a014da244dd1291eaa941235c4a8
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>