PCI: pciehp: Inline the "handle event" functions into the ISR

The pciehp_handle_*() functions (pciehp_handle_attention_button(), etc.)
only contain a line or two of useful code, so it's clumsy to put
them in separate functions.  All they so is add an event to a work queue,
and it's clearer to see that directly in the ISR.

Inline them directly into pcie_isr().  No functional change.

Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
Reviewed-by: Rajat Jain <rajatja@google.com>
Acked-by: Yinghai Lu <yinghai@kernel.org>