msmsteppe_au: Disable aac hw encoder

Change prop to use Android native aac encoder
instead of qcom aac hw encoder.

Suggested-by: Karthik D K

Change-Id: I5d72ee16274195d6250f820ed6b389db8d13d8e1
Signed-off-by: Narsinga Rao Chella <nrchella@codeaurora.org>