irq: provide debug_poll_all_shared_irqs() method under CONFIG_DEBUG_SHIRQ

Provide a shared interrupt debug facility under CONFIG_DEBUG_SHIRQ:
it uses the existing irqpoll facilities to iterate through all
registered interrupt handlers and call those which can handle shared
IRQ lines.

This can be handy for suspend/resume debugging: if we call this function
early during resume we can trigger crashes in those drivers which have
incorrect assumptions about when exactly their ISRs will be called
during suspend/resume.

Signed-off-by: Ingo Molnar <mingo@elte.hu>