ARM: dts: Add basic support for TMDSEVM3730 (Mistral AM/DM37x EVM)

I've tested the serial, MMC, smsc911x, wl12xx, and off-idle support
with the pinctrl patches, so it probably works better than the
board-*.c files ever did. Also the board-omap3evm.c file is broken
for the DSS, and has been for a while. Patches are welcome to fix
it in this .dts file, let's just drop the board-*.c file for this.

Note that off-idle currently requires doing request_irq() on the
wake-up pin from pinctrl-single IRQ domain until we can handle
that in some Linux generic way.

[tony@atomide.com: updated for make dtbs build fix]
Signed-off-by: Tony Lindgren <tony@atomide.com>