FROMLIST: arm64: tls: Avoid unconditional zeroing of tpidrro_el0 for native tasks

When unmapping the kernel at EL0, we use tpidrro_el0 as a scratch register
during exception entry from native tasks and subsequently zero it in
the kernel_ventry macro. We can therefore avoid zeroing tpidrro_el0
in the context-switch path for native tasks using the entry trampoline.

Reviewed-by: Mark Rutland <mark.rutland@arm.com>
Tested-by: Laura Abbott <labbott@redhat.com>
Tested-by: Shanker Donthineni <shankerd@codeaurora.org>
Signed-off-by: Will Deacon <will.deacon@arm.com>
(cherry picked from git://git.kernel.org/pub/scm/linux/kernel/git/arm64/linux.git


 commit 18011eac28c7cb31c87b86b7d0e5b01894405c7f)
[ghackmann@google.com:
 - adjust context
 - replace task_user_tls() accessor with equivalent field from 3.18]
Signed-off-by: Greg Hackmann <ghackmann@google.com>
Change-Id: Ib1ffb34e6f3a722ca111a8fb1811cbc79ffd22fe
Git-Commit: f47c91dc
Git-repo: git://android.googlesource.com/kernel/common.git


[vinmenon@codeaurora.org: trivial merge conflicts]
Signed-off-by: Vinayak Menon <vinmenon@codeaurora.org>