arch: arm: Fix up_interrupt_context() for SMP

Summary:
- I found an issue with up_interrupt_context() when testing.
- And finally found that up_interrupt_context() is not atomic.
- This commit fixes the issue

Impact:
- Affects SMP only

Testing:
- Tested with spresense:wifi_smp and sabre-6quad:smp (qemu)

Signed-off-by: Masayuki Ishikawa <Masayuki.Ishikawa@jp.sony.com>

arch/arm/src/common/arm_interruptcontext.c

@@ -59,5 +59,15 @@
 
 bool up_interrupt_context(void)
 {
-  return CURRENT_REGS != NULL;
+#ifdef CONFIG_SMP
+  irqstate_t flags = up_irq_save();
+#endif
+
+  bool ret = CURRENT_REGS != NULL;
+
+#ifdef CONFIG_SMP
+  up_irq_restore(flags);
+#endif
+
+  return ret;
 }