arm/dts: OMAP3: Add SPI controller nodes

Add the 4 McSPI controller nodes present in an OMAP3 device.

Signed-off-by: Benoit Cousson <b-cousson@ti.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Acked-by: Rob Herring <rob.herring@calxeda.com>