arm64: add spinlock implementation

Provide a simple spinlock implentation for arm64. A value
of 0 is unlocked and a value of 1 is locked.

BUG=chrome-os-partner:31761
BRANCH=None
TEST=Built and ran SMP bringup on ryu.

Change-Id: Ie88a715a6b51cd38a5fdd830583dae528cc49d67
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 14dab94610c96d6b1530c64d661833f8e613101c
Original-Change-Id: I3bf2d80b91112d04442455ff0fa3f16900b7327f
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/216923
Original-Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: http://review.coreboot.org/9040
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/arch/arm64/include/armv8/arch/smp/spinlock.h

@@ -1,6 +1,29 @@
 #ifndef ARCH_SMP_SPINLOCK_H
 #define ARCH_SMP_SPINLOCK_H
 
-#error "spinlocks: implement this for ARM64"
+#include <arch/barrier.h>
+#include <stdint.h>
+
+typedef struct {
+	volatile uint32_t lock;
+} spinlock_t;
+
+#define SPIN_LOCK_UNLOCKED (spinlock_t) { 0 }
+#define DECLARE_SPIN_LOCK(x) static spinlock_t x = SPIN_LOCK_UNLOCKED;
+
+static inline void spin_lock(spinlock_t *spin)
+{
+	while (1) {
+		if (load_acquire_exclusive(&spin->lock) != 0)
+			continue;
+		if (store_release_exclusive(&spin->lock, 1))
+			break;
+	}
+}
+
+static inline void spin_unlock(spinlock_t *spin)
+{
+	store_release(&spin->lock, 0);
+}
 
 #endif