qcom-sps-dma: Avoid re-allocation of pre-allocated resources

Descriptors and channel resources need not be re-allocated every
time BAM pipe is connected.

Change-Id: I0e6cbf07b1815615bb8e0b56d16d87cd57713470
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>
Signed-off-by: Gilad Avidov <gavidov@codeaurora.org>
Signed-off-by: Naveen Kaje <nkaje@codeaurora.org>