Define an enum for gpt timer device type in include/soc/imx/timer.h to
tell the gpt block differences among SoCs.  Update non-DT users (clock
drivers) to pass the device type.

As we now have include/soc/imx/timer.h, the declaration of
mxc_timer_init() is moved into there as the best fit.
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

The revision definitions and declarations are widely used by clock
drivers.  As a step of moving clock drivers out of arch/arm/mach-imx,
let's create header include/soc/imx/revision.h to accommodate them.
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>