mxc_spi: move machine specifics into CPU headers

Move (E)CSPI register declarations into the imx-regs.h files for each supported CPU

Introduce two new macros to control conditional setup
     MXC_CSPI - Used for processors with the Configurable Serial Peripheral Interface (MX3x)
     MXC_ECSPI - For processors with Enhanced Configurable... (MX5x, MX6x)

Signed-off-by: Eric Nelson <eric.nelson@boundarydevices.com>
Acked-by: Dirk Behme <dirk.behme@de.bosch.com>
Acked-by: Stefano Babic <sbabic@denx.de>
Acked-by: Jason Liu <jason.hui@linaro.org>
Tested-by: Jason Liu <jason.hui@linaro.org>