msm: gdsc: Add GDSC regulator driver for msm-copper

Like the 'footswich-8x60' driver for previous generations of MSM
chipsets, the GDSC driver controls power rails associated with
peripheral cores within the SoC. These rails can be enabled and
disabled as required using the regulator framework's APIs.

Change-Id: I2fadb85c002d4e42e9518b32c0fb14b7813903e3
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>