drivers/block/umem: minor cleanups

* tab-align DRIVER_*, pci_driver entries

* reduced wasted memory by killing unused struct cardinfo members

* move free_irq() call above resource unmap, to fix tiny window where
  irq handler may access recently-unmapped memory

* propagate pci_enable_device() return value

* use pci_request_regions, pci_release_regions() for resource reservation

* call pci_disable_device() in pci_driver::remove()

Signed-off-by: Jeff Garzik <jeff@garzik.org>