pci: msm: Add support to send vote against DRV PC

Some endpoints require to prevent DRV processor power
collapse in order to meet the latency requirement to
access DDR over PCIe link. Send the vote info as part
of DRV enable command over rpmsg.

Change-Id: Iac3e6a0cd4978be877ae305aad31ed02570e4f3c
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>