Revert "arm64: optimized copy_to_user and copy_from_user assembly code"

Reverting this commit 6d5031fb since it seems to be causing
regression in some usecases of copy_to_user.

Change-Id: I42a71b85b7a912944e5d3f21a0a2e9db2ff5b465
Signed-off-by: Trilok Soni <tsoni@codeaurora.org>