arm64: defconfig: enable stub-regulator driver for msmskunk

Enable the stub-regulator driver so that regulator consumers
can successful request handles to msmskunk stub-regulator
devices.

Change-Id: Idb6303a00bd441a6dbed2631f8b3a3502fca931e
CRs-Fixed: 1055890
Signed-off-by: David Collins <collinsd@codeaurora.org>