Don't use dlopen() for libebl modules

Don't use dlopen() for libebl modules

Currently, architecture-specific code for libebl exists in separate
libebl_$ARCH.so libraries which libebl loads with dlopen() at runtime.
This makes it impossible to have standalone, statically-linked binaries
which use libdwfl if they depend on any architecture-specific
functionality. Additionally, when these libraries cannot be found, the
failure modes are non-obvious. So, let's get rid of libebl_$arch.so and
move it all into libdw.so/libdw.a, which simplifies things considerably.

Signed-off-by: Omar Sandoval <osandov@fb.com>