qcom: ramdump: Allow callers to specify segment virtual mappings

Memory allocation APIs do not necessarily allow memory
to be ioremapped into the kernel address space. Allow drivers
to specify the virtual address of a segment in memory. The
physical addresses of these segments must still be specified
to discourage drivers from using the ramdump API to dump any
random virtual address space. This will also keep the API
backward compatible.

Change-Id: I149527b84711c5b655fc8f1565a6863444634ef1
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>