Currently, the ISR in the EDMA driver clears the pending interrupt for all
channels without regard to whether that channel has a registered callback
or not.

This causes problems for devices like DM355/DM365 where the multimedia
accelerator uses EDMA by polling on the interrupt pending bits of some of the
EDMA channels. Since these channels are actually allocated through the Linux
EDMA driver (by an out-of-kernel module), the same shadow region is used by
Linux and accelerator. There a race between the Linux ISR and the polling code
running on the accelerator on the IPR (interrupt pending register).

This patch fixes the issue by making the ISR clear the interrupts only for
those channels which have interrupt enabled. The channels which are allocated
for the purpose of being polled on by the accelerator will not have a callback
function provided and so will not have IER (interrupt enable register) bits set.

Tested on DM365 and OMAP-L137/L138 with audio and MMC/SD (as EDMA users).
Signed-off-by: Anuj Aggarwal <anuj.aggarwal@ti.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>
CC: Archith John Bency <archith@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>