The Amazon Model No. D00901 Kindle3 is an E-Book reader based on the
i.MX35 SOC. The device boots in internal boot mode from a build-in eMMC,
alternatively the device may be set into USB-downloader mode when the
Vol+ key is pressed on startup.

Add support for this device and make barebox a drop-in replacement for
the factory shipped u-boot image.
Constraints for the use as drop-in replacement:
- imximg header (offset 0x400) has a maximum size of 2kB minus 16 byte
  since the last 16 bytes are used to store a vendor specific hardware
  desctription identifier
- the bootloader space (application plus env) is limited to 256kB minus
  16 bytes when installed with offset of 4kB (the u-boot offset was 3kB).
  A vendor specific device identifier is stored in the gap between
  application and kernel. The vendor specific identifiers should not
  be overwritten.

Notable features:
- Support for eMMC, USB, UART, I2C, SPI and Keys (except keyboard)
- Full support for vendor specific ATAGs
- usbserial barebox console access by pressing Select button at startup,
  alternatively full console support on connector J14.

Signed-off-by: Alexander Kurz <akurz@blala.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>