irqchip/csky: fixup handle_irq_perbit break irq

The handle_irq_perbit function loop every bit in hwirq local variable.

handle_irq_perbit(hwirq) {
  for_everyt_bit_in(hwirq) {
	handle_domain_irq()
		->irq_exit()
		->invoke_softirq()
		->__do_softirq()
		->local_irq_enable() // Here will cause new interrupt.
  }
}

When new interrupt coming at local_irq_enable, it will finish another
interrupt handler and pull down the interrupt source. But hwirq is the
local variable for handle_irq_perbit(), it can't get new interrupt
controller pending reg status. So we need update hwirq with pending reg
in every loop.

Also change write_relax to writel could prevent stw from fast retire.
When local_irq is enabled, intc regs is really set-in.

Signed-off-by: Guo Ren <ren_guo@c-sky.com>
Cc: Lu Baoquan <lu.baoquan@intellif.com>