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

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

commit 18011eac28c7 upstream.

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>
Signed-off-by: Alex Shi <alex.shi@linaro.org>
Conflicts:
	fold tls_preserve_current_state() in arch/arm64/kernel/process.c