hal: Extend MULTIPLE_OFFLOAD_ENABLED ifdef

* Fixes compilation for non-MSM8974 devices without
  MULTIPLE_OFFLOAD_ENABLED

Change-Id: I8a83d10e68618e141a128af5198ebf1bfb731a6a
hal: PCM offload shouldn't enable all types of offloading

 * Some older versions of the DSP cannot offload audio streams
   for A/V content. Remove the extra check so each feature must
   be explicitly enabled on the device.

Change-Id: I23aac6be5bd160b61e54eab8761e97bbbd5ae045
hal: Fix the samplerate/bitwidth comparison

Change-Id: If507ee28d4b3333dd91af286f2653554590fd7c4
hal: Avoid unnecessary rerouting for sample rate changes

 * The backend codec supports just a few sample rates directly,
   so make sure that we base our decision to reroute on this
   value instead of the actual sample rate of the stream.

Change-Id: I2ed82354563f60d04febb0e200252d0f45644a5e