dma/imx-sdma: save irq flags when use spin_lock in sdma_tx_submit

mx53_loco: fix deadlock report from sdma_tx_submit() during boot

BugLink: http://bugs.launchpad.net/bugs/878701



Adjust to use spin_lock_irqsave()/spin_unlock_irqresotre(), so to
make it safe when called from interrupt context.

Signed-off-by: Haitao Zhang <haitao.zhang@linaro.org>
Signed-off-by: Eric Miao <eric.miao@linaro.org>
Signed-off-by: Richard Zhao <richard.zhao@linaro.org>
Acked-by: Sascha Hauer <s.hauer@pengutronix.de>
Signed-off-by: Vinod Koul <vinod.koul@linux.intel.com>