board: Add new Samsung "stemmy" board based on ST-Ericsson U8500

board: Add new Samsung "stemmy" board based on ST-Ericsson U8500

The ST-Ericsson U8500 SoC has been used in mass-production for
some Android smartphones released around 2012.
In particular, Samsung has released more than 5 different
smartphones based on U8500, e.g.

  - Samsung Galaxy S III mini (GT-I8190) "golden"
  - Samsung Galaxy S Advance (GT-I9070)  "janice"
  - Samsung Galaxy Xcover 2 (GT-S7710)   "skomer"

and a few others.

Mainline Linux has great support for the Ux500 SoC, so these
smartphones can also run Linux mainline quite well.

Unfortunately, the original Samsung bootloader used on these devices
has limitations that prevent booting Linux mainline directly.
It keeps the L2 cache enabled, which causes Linux to crash very early,
shortly after decompressing the kernel.

Using U-Boot allows to circumvent these limitations. We can let the
Samsung bootloader chain-load U-Boot and U-Boot locks the L2 cache
before booting into Linux. U-Boot has several other advantages
- it supports device-trees directly and we are no longer limited to
flashing Android boot images through Samsung's proprietary download
mode.

The Samsung "stemmy" board covers all Samsung devices based on U8500.
Add minimal support for "stemmy". For now only UART is supported but
this will be extended later.

Signed-off-by: Stephan Gerhold <stephan@gerhold.net>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>