msm: mhi_dev: Do not enable aggregated MHI_A7 interrupt

Do not enable the aggregated mhi_a7 irq, and avoid registering
for the corresponding callback if the separate mhi_a7 irq is
supported by the HW to avoid scheduling the workqueue twice for
a single occurrence of the interrupt and to avoid
unbalanced mhi irq enable.

Change-Id: I80ea4e04d9df705bd7c83f117b76c5d5fbbd6ef1
Signed-off-by: Siva Kumar Akkireddi <sivaa@codeaurora.org>