ARM: dts: am437x-sk-evm.dts: fix LCD timings

The lcd0 node for am437x-sk-evm.dts contains bad LCD timings, and while
they seem to work with a quick test, doing for example blank/unblank
will give you a black display.

This patch updates the timings to the 'typical' values from the LCD spec
sheet.

Also, the compatible string is completely bogus, as
"osddisplays,osd057T0559-34ts" is _not_ a 480x272 panel. The panel on
the board is a newhaven one. Update the compatible string to reflect
this. Note that this hasn't caused any issues, as the "panel-dpi"
matches the driver.

Cc: <stable@vger.kernel.org> # v3.17+
Tested-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>