ARM: dts: at91: Add dts files for at91sam9n12ek

ARM: dts: at91: Add dts files for at91sam9n12ek

The device tree source files of at91sam9n12ek boards are copied from
the Linux v4.10, do the changes as below.
 - Add the reg property for the pinctrl node.
 - Move the gpio (pioA, pioB, pioC, pioD) nodes as the pinctrl's
   slibling nodes, instead of the child nodes.
 - Change the compatible of the spi flash to "spi-flash".
 - Add the spi0 aliases.
 - Fix the pinctrl-names of mmc0 node.
 - Add the "u-boot,dm-pre-reloc" property to determine which nodes
   are used by the board_init_f stage.
 - Fix the compilation warnings.

Signed-off-by: Wenyou Yang <wenyou.yang@atmel.com>
Reviewed-by: Simon Glass <sjg@chromium.org>