regulator: cpr-regulator: make qcom,cpr-fuse-bp-cpr-disable prop optional

Update the cpr-regulator driver and documentation in order to
make the qcom,cpr-fuse-bp-cpr-disable device tree property
optional.  Some targets do not allocate a fuse bit for the
purpose of disabling CPR so this property cannot be considered
required.

Change-Id: I39aa59e92585c87b97714fc1684b17f3b9c0523f
Signed-off-by: David Collins <collinsd@codeaurora.org>