dmaengine: at_hdmac: replace spin_lock* with irqsave variants

dmaengine routines can be called from interrupt context and with
interrupts disabled. Whereas spin_unlock_bh can't be called from
such contexts. So this patch converts all spin_lock* routines
to irqsave variants.

Also, spin_lock() used in tasklet is converted to irqsave variants,
as tasklet can be interrupted, and dma requests from such interruptions
may also call spin_lock.

Idea from dw_dmac patch by Viresh Kumar.

Signed-off-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Signed-off-by: Vinod Koul <vinod.koul@intel.com>