arm64: neon: Export kernel_neon_busy to loadable modules

may_use_simd() can be invoked from loadable modules and it accesses
kernel_neon_busy. Make sure that the latter is exported.

Fixes: cb84d11e ("arm64: neon: Remove support for nested or hardirq kernel-mode NEON")
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>

arch/arm64/kernel/fpsimd.c

@@ -255,6 +255,7 @@ void fpsimd_flush_task_state(struct task_struct *t)
 #ifdef CONFIG_KERNEL_MODE_NEON
 
 DEFINE_PER_CPU(bool, kernel_neon_busy);
+EXPORT_PER_CPU_SYMBOL(kernel_neon_busy);
 
 /*
  * Kernel-side NEON support functions