x86: Make dl-cache.h and readelflib.c not Linux-specific

These files could be useful to any port that wants to use ld.so.cache.

Signed-off-by: Sergey Bugaev <bugaevc@gmail.com>
Reviewed-by: Adhemerval Zanella  <adhemerval.zanella@linaro.org>

diff --git a/sysdeps/unix/sysv/linux/x86/readelflib.c b/sysdeps/x86/readelflib.c
similarity index 100%
rename from sysdeps/unix/sysv/linux/x86/readelflib.c
rename to sysdeps/x86/readelflib.c

diff --git a/sysdeps/unix/sysv/linux/x86_64/dl-cache.h b/sysdeps/x86_64/dl-cache.h
similarity index 100%
rename from sysdeps/unix/sysv/linux/x86_64/dl-cache.h
rename to sysdeps/x86_64/dl-cache.h