omap2plus_defconfig: enable the usual drivers

Signed-off-by: Nishanth Menon <nm@ti.com>
ARM: dts: Add am57xx-beagle-x15

BeagleBoard-X15 is the next generation Open Source Hardware
BeagleBoard based on TI's AM5728 SoC featuring dual core 1.5GHZ A15
processor. The platform features 2GB DDR3L (w/dual 32bit busses),
eSATA, 3 USB3.0 ports, integrated HDMI (1920x108@60), separate LCD
port, video In port, 4GB eMMC, uSD, Analog audio in/out, dual 1G
Ethernet.

For more information, refer to: http://www.elinux.org/Beagleboard:BeagleBoard-X15

Just add basic support for the moment, the following updates are needed:
a) DDR size is yet to be ascertained.
b) Enable following peripherals:
  i)	Ethernet
  ii)	HDMI
  iii)	Audio
  iv)	PCI (serdes clk?)

Signed-off-by: Felipe Balbi <balbi@ti.com>
Signed-off-by: Nishanth Menon <nm@ti.com>