arm64/kdump: Build fix for CONFIG_KEXEC

Compilation/Build fix when CONFIG_KEXEC is enabled
This is caused because of :
   a) commit 6c4d635c ("Revert "arm64: kill flush_cache_all()"")
   included internally adds asm code for cpu_soft_restart and defined
   in proc-fns.h. It was added so that ramdump contains all dirty
   cache data and cache flush in reboot.

   b) commit f9076ecf ("arm64: Add back cpu reset routines") from
   upstream adds cpu_soft_restart in cpu_reset.h and hooks it up to
   hyp-stub. This patch's main intention was to add support for kexec.

   The patch chooses to rename function in (b) because it's intended
   use is for kexec.

Change-Id: Ide95220b5f609a82eaf3fcb64c155080be0f39dd
Signed-off-by: Prateek Sood <prsood@codeaurora.org>
Signed-off-by: Akshay Adiga <aadiga@codeaurora.org>