ARM: dts: msm: add qcom,init-voltage-corner for VDD_GFX on msm8994

Specify a default voltage corner value of 3 (SVS SOC) for the VDD_GFX
supply regulator pmi8994_s2_corner since no consumer will be requesting
any specific voltage corner value. This is needed since the RPM will
only enable the VDD_GFX regulator if some corner value is passed along
with the enable request.

Change-Id: Ibb887d74afd7fa3f29d450568e9bffe7b6aea6ed
Signed-off-by: David Keitel <dkeitel@codeaurora.org>