adsprpc: optimize number of SGL entries during map create

Set proper DMA segment size and boundary during mem map creation
to reduce number of SGL entries to 1.

Change-Id: I92392e62766c83ab49a4ec217e5762d5601af425
Acked-by: Thyagarajan Venkatanarayanan <venkatan@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>