The crypto modules for RPi2/3 has chacha20 enabled as a module but not chacha20poly1305. Given the fact that chacha20 is not AEAD, and RPi2/3 does not have ARM-NI available, enabling chacha20-poly1305 would be a good replcement for CPU-consuming GCM cryptos.
[alarm@alarmpi ~]$ uname -a
Linux alarmpi 4.14.33-2-ARCH #1 SMP Wed Apr 11 01:39:04 UTC 2018 armv7l GNU/Linux
[alarm@alarmpi ~]$ sudo pacman -Q | grep linux
libutil-linux 2.32-3
linux-api-headers 4.14.8-1
linux-firmware 20180314.4c0bf11-1
linux-raspberrypi 4.14.33-2
util-linux 2.32-3
[alarm@alarmpi ~]$ zgrep CHACHA20 /proc/config.gz
# CONFIG_CRYPTO_CHACHA20POLY1305 is not set
CONFIG_CRYPTO_CHACHA20=m
CONFIG_CRYPTO_CHACHA20_NEON=m
[alarm@alarmpi ~]$