MLK-9957 mtd: NAND: fix the kernel panic issue for NAND suspend/resume

The branch determined by GPMI_IS_MX6SX() should not include
acquire_dma_channels() function which causes unbalanced dma
request/release on other platform.

Removed GPMI_IS_MX6SX() to make code simple although it is not necessary
to restore GPMI/BCH registers for i.MX6Q/DL

Signed-off-by: Allen Xu <b45815@freescale.com>
(cherry picked from commit 54cd0fe03180dc44e3783bca1546e61d698abd2f)