mhi: cntrl: qcom: enable pm runtime in mission mode only

Runtime suspend only supported while controller is in Mission
mode.

CRs-Fixed: 2457862
Change-Id: I9326539c173e8114fa52344db4546c080d6f7769
Acked-by: Bhaumik Vasav Bhatt <bbhatt@qti.qualcomm.com>
Signed-off-by: Sujeev Dias <sdias@codeaurora.org>