dma_free_coherent() needs irqs enabled (sigh)

On at least ARM (and I'm told MIPS too) dma_free_coherent() has a newish
call context requirement: unlike its dma_alloc_coherent() sibling, it may
not be called with IRQs disabled.  (This was new behavior on ARM as of late
2005, caused by ARM SMP updates.) This little surprise can be annoyingly
driver-visible.

Since it looks like that restriction won't be removed, this patch changes
the definition of the API to include that requirement.  Also, to help catch
nonportable drivers, it updates the x86 and swiotlb versions to include the
relevant warnings.  (I already observed that it trips on the
bus_reset_tasklet of the new firewire_ohci driver.)

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>
Cc: David Miller <davem@davemloft.net>
Acked-by: Russell King <rmk@arm.linux.org.uk>
Cc: Andi Kleen <ak@suse.de>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>