utils: enhance readelf command call with llvm

utils: enhance readelf command call with llvm

Replace `${HOST_PREFIX}readelf` with `${READELF}`.

When utilizing llvm for compiling packages, the invocation of GNU readelf
will consistently occur if the oe_soinstall and oe_libinstall functions,
which are defined in utils.bbclass, are called. This behavior is unfriendly
to llvm. So prefer `${READELF}` over `${HOST_PREFIX}readelf`.

Signed-off-by: lixiaoyong <lixiaoyong19@huawei.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>