imx: discard duplicated MXC_OCOTP and CMD_FUSE

We have CONFIG_MXC_OCOTP and CONFIG_CMD_FUSE in mx6_common.h,
discard duplicated macro definitions in board header files.

Signed-off-by: Peng Fan <Peng.Fan@freescale.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Peter Robinson <pbrobinson@gmail.com>
Cc: Otavio Salvador <otavio@ossystems.com.br>