arm: Remove unused ST-Ericsson u8500 arch

This arch does not seem to be supported / used at all in the current
U-Boot mainline source tree any more. So lets remove the core u8500 code
and code that was only referenced by this platform.

Please note that this patch also removes these config options:

- CONFIG_PL011_SERIAL_RLCR
- CONFIG_PL011_SERIAL_FLUSH_ON_INIT

As they only seem to be referenced by u8500 based boards. Without any
such board in the current code, these config option don't make sense
any more. Lets remove them as well.

If someone still wants to use this platform, then please send patches
to re-enable support by adding at least one board that references this
code.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Mathieu Poirier <mathieu.poirier@linaro.org>
Cc: John Rigby <john.rigby@linaro.org>
Cc: Simon Glass <sjg@chromium.org>
Cc: Masahiro Yamada <yamada.masahiro@socionext.com>
Cc: Tom Rini <trini@konsulko.com>
Cc: Heiko Schocher <hs@denx.de>
Cc: Albert Aribaud <albert.u.boot@aribaud.net>
Reviewed-by: Masahiro Yamada <yamada.masahiro@socionext.com>