Reason for use sw-interrupt as syscall interrupt:
The xtensa `syscall` instruction can cause SYSCALL interrupt.
But SYSCALL interrupt is same interrupt level with level-one
interrupt.
Nuttx swint can enter `enter_critical_section` and gerenate
interrupt.
Signed-off-by: zhuyanlin <zhuyanlin1@xiaomi.com>
Reason: xtensa svcall only have level-1 interrupt level.
Sush do not generate interrupt when up_irq_save.
Software int can generate interrupt when up_irq_save.
Signed-off-by: zhuyanlin <zhuyanlin1@xiaomi.com>
