[ZRAM] added thanks to PLi.

Enable the zram device. Experimental feature to make more memory
available in particular on low-memory boxes.
Read wikipedia or LWN if you want to know more.

Quick guide:
echo 64M > /sys/block/zram0/disksize
mkswap /dev/zram0
swapon /dev/zram0

Override zram recipe to work with our embedded system

Remove bash script requirement
Remove unneeded RDEPENDS
Use a FACTOR of 50 instead of 90
Use only a single CPU