arm: Break cyclic percpu include

In order to use <asm/percpu.h> in irqflags.h, we need to make sure
asm/percpu.h does not itself depend on irqflags.h.
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Will Deacon <will@kernel.org>
Link: https://lkml.kernel.org/r/20200623083721.454517573@infradead.org

arch/arm/include/asm/percpu.h

@@ -5,6 +5,8 @@
 #ifndef _ASM_ARM_PERCPU_H_
 #define _ASM_ARM_PERCPU_H_
 
+register unsigned long current_stack_pointer asm ("sp");
+
 /*
  * Same as asm-generic/percpu.h, except that we store the per cpu offset
  * in the TPIDRPRW. TPIDRPRW only exists on V6K and V7

arch/arm/include/asm/thread_info.h

@@ -75,11 +75,6 @@ struct thread_info {
 	.addr_limit	= KERNEL_DS,					\
 }
 
-/*
- * how to get the current stack pointer in C
- */
-register unsigned long current_stack_pointer asm ("sp");
-
 /*
  * how to get the thread information struct from C
  */