defconfig: kona: enable rpmh-regulator driver

Enable the rpmh-regulator driver so that consumers can make
regulator requests which are handled by VRM and ARC RPMh
accelerators.

Change-Id: I0e3986f15a800db5f8333b7ebb2a63e6eb3854b4
Signed-off-by: David Collins <collinsd@codeaurora.org>