ARM: 6876/1: Kconfig.debug: Remove unused CONFIG_DEBUG_ERRORS

This config option isn't actually used anywhere and can be safely
removed. The last user was traps.c before commit 082f47a ([ARM]
always allow dump_stack() to produce a backtrace, 2007-07-05).

Reviewed-by: Jesper Juhl <jj@chaosbits.net>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>