mtd: msm_qpic_nand: use polling for bam operations

NAND DMA transfers take a very small amount of time. So if interrupts
were used, there will be overhead from both hardware and software
for the interrupt to be passed along to the necessary software. Since
NAND device throughputs are usually low, this overhead will affect NAND
throughput.

If instead of interrupts, the NAND driver was to poll the DMA hardware
for transfer completion, then there will be improvement in NAND
perofrmance.

LMDD throughput testing shows the following throughput improvements

Performance Mode
--------------------------------
	|	Interrupts	|	Polling
Read	|	7.09 MBps	|	8.24 MBps
Write	|	5.31 MBps	|	5.87 MBps

Ondemand Mode
--------------------------------
	|	Interrupts	|	Polling
Read	|	5.45 MBps	|	8.19 MBps
Write	|	4.36 MBps	|	5.77 MBps

This clearly shows that polling gives better performance.

Change-Id: I8e95ebb8a77abc33b793123abc75955b203aa6c1
Signed-off-by: Krishna Konda <kkonda@codeaurora.org>