audio: Supress redundant effect config events in short duration

Distortion sound persists for the whole song when re-enabling effect in
LPA playback mode till switch to next song. And pop noise is quite obvious
when enable/disable effects in LPA.

As the design of LPA, EffectsThreadEntry() loop is used to handle effect
config changes through applying effects with new config on dsp pcm buffers.
However, it can't handle too many config change events in a short time,
and effect with new configuration will be applied on part of dsp buffers.

Filter out redundant effect config events that come too closely to avoid
applying effect on dsp buffer in vain.

Change-Id: If8915b1d068724d5976e1519ec57e3c08cf89c9d
CRs-Fixed: 562806, 563418
audioflinger: SRS effects are not working for LPA

    -Issue: If SRS effects are applied on LPA playback,
     in ARM side there is a delay of 4-5 seconds for effects
     application
    -Root cause: In applyEffects SRS effects are applied first and
     then Android effects are applied.
     In case of active android effects, SRS effects are called
     first and then android effects are called, so buffer with
     SRS effects is getting overwritten with buffer with
     android effects.
     If there are no android effects applied then all
     the SRS effects are overwritten with decoded data.
     So until next write call, SRS effects are not applied and hence delay
     of 4-5 seconds
    -Fix: In applyEffects first apply android effects and then
     apply SRS effects

Change-Id: I36b2133256d168f06b13c3d4a2bad00312d571ac
CRs-Fixed: 566278
audio: Initialize LPA variables in audioflinger

 - During initialization of audioflinger, a number of
variables related to LPA are not set to default values.
This causes an undesired side effect that the first
effect in the effect chain is considered to be LPA
enabled. Since LPA does not execute effect processing,
switching xLoud on/off does nothing
 - Fixed by initializing member variables in audioflinger.

Change-Id: Ide06fb0e6804558388e6610cc7686f168591e4a5
Merge remote-tracking branch 'CyanogenMod/cm-10.2' into cm-10.2