ARM: OMAP2+: Drop sdma interrupt handling for mach-omap2

All device tree probing omap SoCs only have device drivers that are using
Linux dmaengine API with the IRQENABLE_L1 interrupts. Only omap1 is still
using old legacy dma.

This means we can remove the legacy sdma interrupt handling for
IRQENABLE_L0, and only rely on the dmaengine driver using IRQENABLE_L1.

The legacy code still allocates the channels, but that will be deal with
in the following patches.

Cc: Aaro Koskinen <aaro.koskinen@iki.fi>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Cc: Russell King <rmk+kernel@armlinux.org.uk>
Cc: Vinod Koul <vkoul@kernel.org>
Acked-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Tested-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>