arm64: dts: qcom: Move msm8994-smd-rpm contents to lg-bullhead.

arm64: dts: qcom: Move msm8994-smd-rpm contents to lg-bullhead.

This was the only device using that dtsi, so no point
keeping it separate AND with a confusing name (bullhead
is based on msm8992 and the file contains regulator
values for that specific board).

Signed-off-by: Konrad Dybcio <konradybcio@gmail.com>
Link: https://lore.kernel.org/r/20200624150107.76234-8-konradybcio@gmail.com
[bjorn: Squashed with change that remove regulators from msm8992.dtsi]
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>