ARM: 7584/1: perf: fix link error when CONFIG_HW_PERF_EVENTS is not selected

Commit e50c541 (ARM: perf: add guest vs host discrimination) broken the
link as perf_instruction_pointer and perf_misc_flags are not defined
when CONFIG_HW_PERF_EVENTS is not selected.

As it make little sense to try and profile a guest without any HW event,
just fallback to the original code when this config option is not selected.

Reported-by: Russell King <linux@arm.linux.org.uk>
Acked-by: Will Deacon <will.deacon@arm.com>
Signed-off-by: Marc Zyngier <marc.zyngier@arm.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>

arch/arm/include/asm/perf_event.h

@@ -21,9 +21,11 @@
 #define C(_x)				PERF_COUNT_HW_CACHE_##_x
 #define CACHE_OP_UNSUPPORTED		0xFFFF
 
+#ifdef CONFIG_HW_PERF_EVENTS
 struct pt_regs;
 extern unsigned long perf_instruction_pointer(struct pt_regs *regs);
 extern unsigned long perf_misc_flags(struct pt_regs *regs);
 #define perf_misc_flags(regs)	perf_misc_flags(regs)
+#endif
 
 #endif /* __ARM_PERF_EVENT_H__ */