ARM: 8274/1: Fix DEBUG_LL for multi-platform kernels (without PL01X)

When building a multi_v7_defconfig kernel it is not possible to configure
DEBUG_LL to use any serial device except a ARM Primecell PL01X, or more
accurately and worse, it is possible to configure a different serial
device but KConfig does not honour this request. In fact this also
overrides the user selection for some of the single platform kernels, for
example I don't think DEBUG_LL can be targeted at ICE or semihosted
supervisor for ARCH_VERSATILE.

This happens because DEBUG_UART_PL01X is automatically enabled by
some architectures and this means user decisions made regarding
the DEBUG_LL backend will be overridden. Problem is fixed by removing the
automatic enabling of this option.

Signed-off-by: Daniel Thompson <daniel.thompson@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>