msm: ADSPRPC: Initialize the list for global gfa maps

List initialization for global gfa remote heap maps is
missing. Initializing the same.

Change-Id: Ibe479a0ccc8b829919f5ce92f7ac2f868a546736
Acked-by: Himateja Reddy <hmreddy@qti.qualcomm.com>
Signed-off-by: Tharun Kumar Merugu <mtharu@codeaurora.org>