traps: i386: expand clear_mem_error and remove from mach_traps.h

This is the last user of clear_mem_error, which is defined
only on i386. Expand the inline function and remove it from
include/asm-x86/mach-default/mach_traps.h

Signed-off-by: Alexander van Heukelum <heukelum@fastmail.fm>
Signed-off-by: Ingo Molnar <mingo@elte.hu>