Per Grant's review comment - driver changes via tty tree

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>

* arc-uart platform device now populated dynamically, using
  of_platform_populate() - applies to any other device whatsoever.

* uart in turn requires incore arc-intc to be also present in DT

* A irq-domain needs to be instantiated for IRQ requests by DT probed
  device (e.g. arc-uart)

TODO: switch over to linear irq domain once all devs have been
      transitioned to DT

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: Arnd Bergmann <arnd@arndb.de>

* mem size now runtime configured (prev CONFIG_ARC_PLAT_SDRAM_SIZE)
* core cpu clk runtime configured (prev CONFIG_ARC_PLAT_CLK)

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@secretlab.ca>

This is minimal infrastructure needed for devicetree work.
It uses an a sample "skeleton" devicetree - embedded in kernel image -
to print the board, manufacturer by parsing the top-level "compatible"
string.

As of now we don't need any additional "board" specific "machine_desc".

TODO: support interpreting the command line as boot-loader passed dtb

Signed-off-by: Vineet Gupta <vgupta@synopsys.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Cc: devicetree-discuss@lists.ozlabs.org
Cc: Rob Herring <rob.herring@calxeda.com>
Cc: James Hogan <james.hogan@imgtec.com>
Reviewed-by: Rob Herring <rob.herring@calxeda.com>
Reviewed-by: James Hogan <james.hogan@imgtec.com>