drivers: soc: qcom: Rename wakeup sideband notification

Rename EVT_WAKE_UP to EVENT_REQUEST_WAKE_UP to clearly
expalin that this notification is to request to wake up
the remote processor.

Change-Id: Icc829f3b6c6d8b0cfc2e0ff189a0152759bb6415
Signed-off-by: Shreyas K K <shrekk@codeaurora.org>