Bluetooth: controller: Fix enc. setup during PHY update

If a PHY update is waiting for the instant to be reached and the master
starts the encryption procedure, store the pending PHY update procedure
and handle it simultaneously with the encryption setup.

This fix prevents the encryption setup from stalling and thereby timing
out after 40s, after which the master drops the link.

The ll_conn::llcp::encryption can not longer be unioned with the
ll_conn::llcp:phy_upd_ind as one would overwrite the other.

Signed-off-by: Thomas Ebert Hansen <thoh@oticon.com>