arm64: add cpu_is_bsp() concept

It's helpful to know if the current running CPU
is the BSP. Therefore, provide that semantic.

BUG=chrome-os-partner:32082
BRANCH=None
TEST=Built and booted to kernel.

Change-Id: I18cb8ab5149c3337e22b1f6046b1af266be7e47c
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: b390dc70b658c207cd3b64408713ec4cddab3172
Original-Change-Id: I3d5518d1f6d6a78b14f25bb7ef79727605064561
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/218653
Original-Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: http://review.coreboot.org/9083
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>
3 files changed