slim_ngd: Support reserving message bandwidth for clients

Message bandwidth can be reserved by clients to do message-intensive
transactions over Slimbus. While slimbus framework supports that,
NGD driver was missing corresponding code to send this request to
master driver on ADSP. This patch adds that support.

Change-Id: If6a340746816658ac0aa1b4bd7c2270205eb6d4a
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>