this driver doesn't use any from <plat/dmtimer.h>, so
we can remove it without any problems.

This will, however cause a problem because omap-serial.c
was relying on indirect inclusion of <linux/platform_device.h>,
let's fix the issue by including <linux/platform_device.h>
on omap-serial.c as it should be.
Tested-by: NShubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: NFelipe Balbi <balbi@ti.com>
Signed-off-by: NGreg Kroah-Hartman <gregkh@linuxfoundation.org>