RISC-V: Declare cpu_ops_spinwait in <asm/cpu_ops.h>

The cpu_ops_spinwait is used in a couple of places in arch/riscv
and is causing a sparse warning due to no declaration. Add this
to <asm/cpu_ops.h> with the others to fix the following:

arch/riscv/kernel/cpu_ops_spinwait.c:16:29: warning: symbol 'cpu_ops_spinwait' was not declared. Should it be static?
Signed-off-by: Ben Dooks <ben.dooks@sifive.com>
Link: https://lore.kernel.org/r/20220714071811.187491-1-ben.dooks@sifive.com
[Palmer: Drop the extern from cpu_ops.c]
Fixes: 2ffc48fc ("RISC-V: Move spinwait booting method to its own config")
Cc: stable@vger.kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

arch/riscv/include/asm/cpu_ops.h

@@ -38,6 +38,7 @@ struct cpu_operations {
 #endif
 };
 
+extern const struct cpu_operations cpu_ops_spinwait;
 extern const struct cpu_operations *cpu_ops[NR_CPUS];
 void __init cpu_set_ops(int cpu);
 

arch/riscv/kernel/cpu_ops.c

@@ -15,9 +15,7 @@
 const struct cpu_operations *cpu_ops[NR_CPUS] __ro_after_init;
 
 extern const struct cpu_operations cpu_ops_sbi;
-#ifdef CONFIG_RISCV_BOOT_SPINWAIT
-extern const struct cpu_operations cpu_ops_spinwait;
-#else
+#ifndef CONFIG_RISCV_BOOT_SPINWAIT
 const struct cpu_operations cpu_ops_spinwait = {
 	.name		= "",
 	.cpu_prepare	= NULL,