base: Use system libelf instead of ext

base: Use system libelf instead of ext

The only change needed is to remove EM_SPARC64, which from what I can
tell was removed from elf.h in 1998.

https://sources.debian.org/src/glibc/2.24-11+deb9u1/ChangeLog.8/#L6134

Change-Id: I0dd7e23ea44b19c2ebd9c6eff7cbaedfe69d821b
Signed-off-by: Jason Lowe-Power <jason@lowepower.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/33317
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabeblack@google.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Gabe Black <gabeblack@google.com>