udev: single binary replacing udevd and udevadm

Since the separate binaries contain mostly the same code,
this almost halves the size of the installation.

before:
398K /bin/udevadm
391K /lib/systemd/systemd-udevd

after:
431K /bin/udevadm
0    /lib/systemd/systemd-udevd -> ../../bin/udevadm

Fixes: #14200