arm64: add smp_processor_id() declaration

In order to accomodate MP on arm64 one needs to be able to determine
the current logical processor id. Because it depends on the SoC
implementation the SoC needs to provide this implementation.

BUG=chrome-os-partner:31545
BRANCH=None
TEST=Built.

Change-Id: I2f09df9bf7d4f829d8f45471bf7281a4ddba2fc8
Signed-off-by: Patrick Georgi <pgeorgi@chromium.org>
Original-Commit-Id: 6033e73d70
Original-Change-Id: I9511b54b5a1ab340b0f1309b0d9976be68b50903
Original-Signed-off-by: Aaron Durbin <adurbin@chromium.org>
Original-Reviewed-on: https://chromium-review.googlesource.com/214663
Original-Reviewed-by: Furquan Shaikh <furquan@chromium.org>
Reviewed-on: http://review.coreboot.org/9007
Tested-by: build bot (Jenkins)
Reviewed-by: Stefan Reinauer <stefan.reinauer@coreboot.org>

src/arch/arm64/include/armv8/arch/cpu.h

@@ -40,13 +40,16 @@ struct cpu_info {
 #endif
 };
 
-struct cpuinfo_arm {
-        uint8_t    arm;            /* CPU family */
-        uint8_t    arm_vendor;     /* CPU vendor */
-        uint8_t    arm_model;
-};
-
 #endif
 
 struct cpu_info *cpu_info(void);
+
+/*
+ * Returns logical cpu in range [0:MAX_CPUS). SoC should define this.
+ * Additionally, this is needed early in arm64 init so it should not
+ * rely on a stack. Standard clobber list is fair game: x0-x7 and x0
+ * returns the logical cpu number.
+ */
+unsigned int smp_processor_id(void);
+
 #endif /* __ARCH_CPU_H__ */