If we are softbooting another kernel using kexec, DMA controller state is not
known when we are performing omap_init_dma(). It is possible that some DMA
channels are already active. For example after kexec we get:

<4>IRQ 0020 for non-allocated DMAchannel 5
<4>IRQ 0020 for non-allocated DMAchannel 5
<4>IRQ 0020 for non-allocated DMAchannel 5
<4>IRQ 0020 for non-allocated DMAchannel 5
<4>IRQ 0020 for non-allocated DMAchannel 5

To prevent any weird things happening, we disable all channel interrupts during
init.
Signed-off-by: NMika Westerberg <ext-mika.1.westerberg@nokia.com>
Acked-by: NKevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: NTony Lindgren <tony@atomide.com>