ARM: dts: DRA7: Add the dts files for dra7 SoC and dra7-evm board

Add minimal device tree source needed for DRA7 based SoCs.
Also add a board dts file for the dra7-evm (based on dra752)
which contains 1.5G of memory with 1G interleaved and 512MB
non-interleaved. Also added in the board file are pin configuration
details for i2c, mcspi and uart devices on board.

Signed-off-by: R Sricharan <r.sricharan@ti.com>
Signed-off-by: Rajendra Nayak <rnayak@ti.com>
Signed-off-by: Sourav Poddar <sourav.poddar@ti.com>
Signed-off-by: Benoit Cousson <bcousson@baylibre.com>