qcom: smem: Rework SMEM ramdump logic

SMEM ramdumps should only be transferred if the subsystem
restart framework indicates that ramdumps are enabled.
Furthermore, use the SUBSYS_RAMDUMP_NOTIFICATION notifier
type instead of AFTER_SHUTDOWN.

Change-Id: I8d48add907e57687fa320b4ed80de61a46e27b91
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>