arm64: dts: qcom: qcs6490-rb3gen2: Rename vph-pwr regulator node

arm64: dts: qcom: qcs6490-rb3gen2: Rename vph-pwr regulator node

When fixed regulators are not named with "regulator-" prefix, they can
not be neatly grouped and sorted together.

Rename the vph-pwr-regulator, to facilitate the incoming addition of
additional fixed regulators.

Signed-off-by: Bjorn Andersson <bjorn.andersson@oss.qualcomm.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
Link: https://lore.kernel.org/r/20251102-rb3gen2-regulator-sort-v1-1-908879d240be@oss.qualcomm.com
Signed-off-by: Bjorn Andersson <andersson@kernel.org>