ANDROID: GKI: Revert "arm64: kill flush_cache_all()"

This reverts the upstream commit <68234df4>
("arm64: kill flush_cache_all()"). This is required internally
for certain use-cases like flushing cache before reboot to
ensure all the data is available in the ramdump.

Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>
Signed-off-by: Venkata Narendra Kumar Gutta <vnkgutta@codeaurora.org>
(cherry picked from commit 208984f39cda4c963d052c48862e3e9e0b4dba55)
[surenb: resolve merge conflicts, do not add unused cpu_soft_restart
function because it conflicts with the function of the same name from
arch/arm64/kernel/cpu-reset.h]
Bug: 153349826
Test: build
Signed-off-by: Suren Baghdasaryan <surenb@google.com>
Change-Id: I47b4f4ba4001c1fbb53794c6da0b3fdf641bd981