msm: cpr-regulator: change device tree vendor prefix from 'qti' to 'qcom'

New policy requires changing device tree vendor prefix from 'qti'
to 'qcom'. Also change device tree files for msm8610, msm8226 and msm8926.

Change-Id: I0b00127a698e10c2d937b515cd7e55ae3b0ba569
Signed-off-by: Ke Liu <keliu@codeaurora.org>