arm/pxa2xx: reorgazine SSP and SPI header files

The PXA-SPI driver relies on some files / defines which are arm specific
and are within the ARM tree. The CE4100 SoC which is x86 has also the
SPI core.
This patch moves the ssp and spi files from arm/mach-pxa and plat-pxa to
include/linux where the CE4100 can access them.

This move got verified by building the following defconfigs:
   cm_x2xx_defconfig corgi_defconfig em_x270_defconfig ezx_defconfig
   imote2_defconfig pxa3xx_defconfig spitz_defconfig zeus_defconfig
   raumfeld_defconfig magician_defconfig

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Dirk Brandewie <dirk.brandewie@gmail.com>