dts: rk3399-puma: add DTS for RK3399-Q7 (Puma) SoM

The RK3399-Q7 is a system-on-module featuring the Rockchip RK3399
in a Qseven-compatible form-factor.

These changes add a device-tree describing the board and its
interfaces for basic functionality (e.g. GbE, SPI, eMMC, SD-card).

This includes the following changes from the original development:

 * dts: rk3399-puma: include DTS for RK3399-Q7 SoM in the Makefile
 * dts: rk3399-puma: add gmac for the RK3399-Q7

This change enables the Gigabit Ethernet support on the RK3399-Q7.

 * dts: rk3399-puma: use serial0 for stdout
 * dts: rk3399-puma: prepare the sdmmc node for SPL booting
 * dts: rk3399-puma: enable spi1 and spi5, add /spi1/spiflash

The RK3399-Q7 (Puma) unsually (this is a build-time option for
customised boards) has an on-module SPI-flash connected to SPI1.
As of today, this is a Winbond W25Q32DW (32MBit) device.

The SPI5 controller is routed to the Q7 edge connector and provides
general-purpose SPI connectivity for customer base-boards.

With some minor improvements on integration into our outbound tree
 - explicitly modelled the SPI flash as 'spiflash' under spi0
   [dts: rk3399-puma: explicitly model spi-flash under spi1]
 - renamed the aliases to spi0 and spi1 to allow easier use of
   commands and legacy (SPL) infrastructure... i.e. the controllers
   will be 0 and 1 for 'sf probe', 'sspi', etc.
   [dts: rk3399-puma: rename aliases to number spi as 0 and 1 for commands]

 * dts: rk3399-puma: include SPI in the spl-boot-order property

Signed-off-by: Philipp Tomsich <philipp.tomsich@theobroma-systems.com>
Acked-by: Simon Glass <sjg@chromium.org>