soc: fsl: move cpm.h from powerpc/include/asm to include/soc/fsl

Some drivers, e.g. ucc_uart, need definitions from cpm.h. In order to
allow building those drivers for non-ppc based SOCs, move the header
to include/soc/fsl. For now, leave a trivial wrapper at the old
location so drivers can be updated one by one.

Reviewed-by: Timur Tabi <timur@kernel.org>
Signed-off-by: Rasmus Villemoes <linux@rasmusvillemoes.dk>
Signed-off-by: Li Yang <leoyang.li@nxp.com>