ASoC: qdsp6v2: fallback to system heap only if smmu enabled

When ion alloc fails for audio heap, currently driver falls back
to use system heap. But if SMMU is not enabled, system heap is
not supposed to be used. Add check to avoid fallback to system
heap if SMMU is not enabled.

Change-Id: Iafc34b7dd13edc5272225b36ba97a80842a753cc
Signed-off-by: Laxminath Kasam <lkasam@codeaurora.org>