Added 2 configuration parameters to armbian-zram-config.
First paramter (SWAP=) can explicitely disable zram swap (while leaving log and tmp untouched).
Second parameter (TMP_SIZE) can be used to explicitely set tmp ramdisk size.
The behaviour of existing configurations is not changed.
New function activate_zram() to initialize zram devices and parameters.
Changed script to use zramctl to more flexibly establish zram devices to use for log and tmp.
This also fixes issues which result from both armbian-zram-config and armbian-ramlog being hardcoded to use zram0
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