msm: Kconfig: Introduce a configuration option for krait regulators

Currently the krait-regulator driver is only compiled for 8974 based
devices. krait-regulator devices will be used in other MSMs.

Introduce a config option for the krait-regulator driver.

Change-Id: Ib4a636f940c6b4d22177edd86552399aaf5bd97c
Signed-off-by: Abhijeet Dharmapurikar <adharmap@codeaurora.org>