arm/dt: msm8974: acpuclock: Remove acpuclock pm8941_s2 regulator usage

The RPM processor manages the dependency between the PM8941
SMPS 2 and LDO 12 regulators on MSM8974 targets.  Therefore,
remove the usage of pm8941_s2 in both the MSM8974 device tree
as well as the acpuclock-8974 driver.  The enable requests made
for pm8941_l12 will be propagated to the S2 regulator by the RPM.
Removing the usage of pm8941_s2 means that redundant S2 regulator
requests will not be sent to the RPM.  This will reduce the
latency of some acpuclock operations.

Change-Id: Ib91a750bb3c224516d036c67c37ab586592bb3d4
Signed-off-by: David Collins <collinsd@codeaurora.org>