ARM: dts: qcom: apq8064: Convert adreno from legacy gpu-pwrlevels to opp-v2

APQ8064 was last user of gpu-pwrlevels inside mainline tree, so convert
it now.

Tested on Nexus 7 2013, no functional changes.

Signed-off-by: David Heidelberg <david@ixit.cz>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>
Link: https://lore.kernel.org/r/20210829133918.57780-3-david@ixit.cz