dmaengine: fsl-edma: support little endian for edma driver

Our platforms with below registers(CHCFG0 - CHCFG15) of eDMA
*-----------------------------------------------------------*
|     Offset   | Big endian Register| Little endian Register|
|--------------|--------------------|-----------------------|
|     0x0      |        CHCFG0      |           CHCFG3      |
|--------------|--------------------|-----------------------|
|     0x1      |        CHCFG1      |           CHCFG2      |
|--------------|--------------------|-----------------------|
|     0x2      |        CHCFG2      |           CHCFG1      |
|--------------|--------------------|-----------------------|
|     0x3      |        CHCFG3      |           CHCFG0      |
|--------------|--------------------|-----------------------|
|     ...      |        ......      |           ......      |
|--------------|--------------------|-----------------------|
|     0xC      |        CHCFG12     |           CHCFG15     |
|--------------|--------------------|-----------------------|
|     0xD      |        CHCFG13     |           CHCFG14     |
|--------------|--------------------|-----------------------|
|     0xE      |        CHCFG14     |           CHCFG13     |
|--------------|--------------------|-----------------------|
|     0xF      |        CHCFG15     |           CHCFG12     |
*-----------------------------------------------------------*

Current eDMA driver does not support Little endian, so this
patch is to improve edma driver to support little endian.

Signed-off-by: Peng Ma <peng.ma@nxp.com>
Signed-off-by: Vinod Koul <vkoul@kernel.org>