include/fsl: add common FlexTimer #defines in a separate header.

Several files are/will be using the same #defines to use the Flextimer
module. Regroup them in a common file.

Reviewed-by: Esben Haabendal <esben@haabendal.dk>
Signed-off-by: Patrick Havelange <patrick.havelange@essensium.com>
Signed-off-by: William Breathitt Gray <vilhelm.gray@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>