not enbling spi/uart cape from uEnv.txt in arch-linux

hello everyone,

I have enbled uart/spidev cape from uEnv.txt file from /boot/uboot in debian.

i newly installed arch-linux on BBB

but in boot partition uEnv.txt file content only one line
optargs=coherent_pool=1M

i have tried to load .dtbo(uart/spidev) file from here (like from debian) but not loaded.
cape_enable=capemgr.enable_
partno=BB-SPIDEV1
cape_enable=capemgr.enable_partno=BB-UART1

how edit or add any content to uEnv.txt file like in debian to enable cape @ boot
how can i do uEnv.txt file same as debian

i followed below link to to install arch-linux
http://archlinuxarm.org/platforms/armv7/ti/beaglebone-black