ARM: dts: msm: Change speed bin and cpufreq for mdmfermium

Speed bin number for mdmfermium is 4. Change the speed bin node to
reflect the same. Change minimum CPU frequency to be requested as
806.4 MHz. Modify speed-bin, cpufreq, regulator corner mappings to
reflect the same.

Change-Id: I9792fd17a0c659827688581ce30983571def202c
Signed-off-by: Jaydeep Sen <jsen@codeaurora.org>