ARM: dts: msm: Add a missing frequency to cpubw devices for msm8996

This change updates the cpubw and mincpubw frequency tables with
the additional frequency of 1.296 GHz as per the latest
documentation.

Change-Id: Icb62ae734a5730fd2d597c793f4dea97ec3aabc5
Signed-off-by: Rohit Gupta <rohgup@codeaurora.org>