msm: acpuclock-8960ab: Undervolt by 75uV globally

* Undervolt L2 too.
* Adjust regulator and voltage contro limits to allow
+50mV overvolting and -100mV undervolting.

Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>
msm: acpuclock-8960ab: Add frequency steps to 1.944 GHz

Signed-off-by: Zhao Wei Liew <zhaoweiliew@gmail.com>