tools: refactor HOSTLOADLIBES_* options

The tools mkimage, dumpimage, fit_info, fit_check_sign
always have the common libraries to be linked,
so HOSTLOADLIBES_* can be consolidated a little bit.

Signed-off-by: Masahiro Yamada <yamada.m@jp.panasonic.com>
Acked-by: Simon Glass <sjg@chromium.org>
Series-to: uboot
Series-prefix: RESEND
Commit-notes:
  - Resend as a single patch with Simon's Acked tag.
END