msm: acpuclock-krait: Support scaling CPU current requests

The current acpuclock-krait driver asserts a constant regulator
current request when a CPU is initialized or inserted, and
removes it when a CPU is hotplug-removed.

Improve on this by allowing the current requests to scale based
on the speed of the CPUs. This allows acpuclock drivers to
factor dynamic power into its current requests, which will
change based on the frequency.

Only msm8974 regulators support current requests, so the cur_ua
column is omitted from the other frequency tables. The 8974
table is populated with pessimistic placeholder currents for now,
until characterization data is available.

Change-Id: I1ef89406a0de0038d32039c361b755a5eedba847
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>