rockchip: Add support for RAM boot from maskrom mode

The BootROM in Rockchip SoCs will enter maskrom mode when boot firmware
cannot be found in nand/spi/mmc storage.

In maskrom mode the USB OTG port can accept one of two custom commands.

Initially a 0x471 command to load TPL into SRAM. After TPL has been
executed and it has returned back-to-BROM, a 0x472 command to load SPL
into start of DRAM.

Add two binman images that can be used to RAM boot from maskrom mode:
- u-boot-rockchip-usb471.bin that contains TPL to init DRAM.
- u-boot-rockchip-usb472.bin that contains SPL and the normal FIT
  payload with i.e. U-Boot proper, TF-A and FDT.

A config fragment rockchip-ramboot.config can be used to enable building
of these two binman images, e.g.:

  make generic-rk3588_defconfig rockchip-ramboot.config

These binman images can be used with the proprietary rkbin boot_merger
tool to create a special loader image that can be used with tools such
as rkdeveloptool or rockusb tools to RAM boot from maskrom, e.g.:

  Create loader image:
    $ ../rkbin/tools/boot_merger ./RK3588MINIALL.ini

  Boot from maskrom:
    $ rkdeveloptool db u-boot-rockchip-rk3588-loader.bin
   or
    $ rockusb download-boot u-boot-rockchip-rk3588-loader.bin

Another option that does not require use of proprietary tools is using
open source tools such as rkflashtool or rkusbboot that can load the
binman images directly without any need to first create a special loader
image to RAM boot from maskrom, e.g.:

  $ rkflashtool l < u-boot-rockchip-usb471.bin
  $ rkflashtool L < u-boot-rockchip-usb472.bin
 or
  $ rkusbboot u-boot-rockchip-usb471.bin u-boot-rockchip-usb472.bin

Signed-off-by: Jonas Karlman <[email protected]>
Tested-by: Arnaud Patard <[email protected]>
Reviewed-by: Kever Yang <[email protected]>

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