ARM64: Move xSELF from x18 to x19.

This patch moves xSELF to callee saved x19 and removes support for
ETR (external thread register), previously used across native calls.

Change-Id: Icee07fbb9292425947f7de33d10a0ddf98c7899b
Signed-off-by: Serban Constantinescu <serban.constantinescu@linaro.org>
19 files changed