string: drop redundant declarations

string: drop redundant declarations

These standard functions shouldn't need custom declarations. The only
case where redundancy might be needed is if there were inline functions
there. But we don't have any here (anymore). Prune the per-arch headers
of duplicate declarations while moving the asm/string.h inclusion past
the declarations.

Signed-off-by: Jan Beulich <jbeulich@suse.com>
Acked-by: Julien Grall <jgrall@amazon.com>