defconfig: msm8910: Enable stub-regulator driver

Enable CONFIG_REGULATOR and CONFIG_REGULATOR_STUB so that
stub-regulator devices specified via device tree are probed and
available for use by regulator consumers.

Change-Id: I46995e60422d084c495599b744eefcb070d24cee
Signed-off-by: David Collins <collinsd@codeaurora.org>