Have to install this driver: https://www.archlinux.org/packages/?name=broadcom-wl-dkms
sudo pacman -S linux-headers broadcom-wl-dkms
Then after reboot wlp12s0 device was found:
ip link
1: lo: mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT group default qlen 1000
link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: enp9s0: mtu 1500 qdisc fq_codel state UP mode DEFAULT group default qlen 1000
link/ether 00:25:64:47:bd:bb brd ff:ff:ff:ff:ff:ff
3: wlp12s0: mtu 1500 qdisc fq_codel state UNKNOWN mode DEFAULT group default qlen 1000
link/ether 00:22:5f:d3:14:d2 brd ff:ff:ff:ff:ff:ff
