regulator: Add Kconfig for proxy consumer regulator driver

Commit 2876a34e ("regulator: msm: Add snapshot of regulator
drivers for MSM8996") missed the corresponding Kconfig option for
the proxy consumer regulator driver. Fix this.

Signed-off-by: Osvaldo Banuelos <osvaldob@codeaurora.org>
Change-Id: I2dddf07c02a83a22be2a3813845ed454d9ec1621