ar71xx: Use sysupgrade's RAMFS_COPY_* for fw_(set|print)env

ar71xx: Use sysupgrade's RAMFS_COPY_* for fw_(set|print)env

The install_bin from /lib/upgrade/common.sh is no longer creating the
symlinks when a secondary parameter is added. But the fw_setenv program was
always copied this way to the ramdisk for the upgrade.

Instead, this should be done using RAMFS_COPY_* like on all other
platforms.

Fixes: 438dcbfe74a6 ("base-files: automatically handle paths and symlinks for RAMFS_COPY_BIN")
Signed-off-by: Sven Eckelmann <[email protected]>
(backported from 11d51276b1b0ac6a556a776374ca3de07b062e29)