drm/tilcdc: split reset to a separate function

Split reset to a separate function and use usleep_range(250, 1000)
instead of msleep(1) to to keep the reset bit on long enough.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
[Added description to the patch, changed mdelay(500) to usleep_range(250, 1000)]
Signed-off-by: Jyri Sarha <jsarha@ti.com>