ARM: OMAP: Fix Beagleboard DVI reset gpio

Commit e813a55e ("OMAP: board-files:
remove custom PD GPIO handling for DVI output") moved TFP410 chip's
powerdown-gpio handling from the board files to the tfp410 driver. One
gpio_request_one(powerdown-gpio, ...) was mistakenly left unremoved in
the Beagle board file. This causes the tfp410 driver to fail to request
the gpio on Beagle, causing the driver to fail and thus the DVI output
doesn't work.

This patch removes several boot errors from board-omap3beagle.c:

 - gpio_request: gpio--22 (DVI reset) status -22
 - Unable to get DVI reset GPIO

There is a combination of leftover code and revision confusion.
Additionally, xM support is currently a hack.

For original Beagleboard this removes the double initialization of GPIO
170, properly configures it as an output, and wraps the initialization
in an if block so that xM does not attempt to request it.

For Beagleboard xM it removes reference to GPIO 129 which was part
of rev A1 and A2 designs, but never functioned. It then properly assigns
beagle_dvi_device.reset_gpio in beagle_twl_gpio_setup and removes the
hack of initializing it high. Additionally, it uses
gpio_set_value_cansleep since this GPIO is connected through i2c.

Unfortunately, there is no way to tell the difference between xM A2 and
A3. However, GPIO 129 does not function on rev A1 and A2, and the TWL
GPIO used on A3 and beyond is not used on rev A1 and A2, there are no
problems created by this fix.

Tested on Beagleboard-xM Rev C1 and Beagleboard Rev B4.

Signed-off-by: Russ Dill <Russ.Dill@ti.com>
Acked-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>