defconfig: sdm670: enable regulator proxy consumer driver

Enable the proxy consumer driver so that regulators may be kept
at a certain minimum level during boot.  This allows all
consumers to make their requests without interfering with each
other.

Change-Id: I9d7ff21cca5329dada8a73ed522228ffdcded69c
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>