ARM: dts: msm: remove unused CPU device tree properties for msm8996

For a while now, the PSCI cpu enable method has been selected for 8996.
Going forward, this will be the only tested and supported method. Trim
device tree properties and nodes that are only needed for the
"qcom,msm8996-acc" enable method. Kernel support for this method will
soon be removed.

Change-Id: I8912f198f20f6757077df355bf2d1aeae0ec09d2
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>