Add support for enabling zram in the kernel.

The zram module creates RAM-based block devices named /dev/zram<id> (<id>
= 0, 1, ...). Pages written to these disks are compressed and stored in
memory itself. These disks allow very fast I/O and compression provides
good amounts of memory savings. Some of the use cases include /tmp storage,
use as swap disks, various caches under /var and maybe many more.

Different compression algorithms can be selected which give trade-offs between
speed and compression.

Signed-off-by: Trevor Woerner <twoerner@gmail.com>
Signed-off-by: Bruce Ashfield <bruce.ashfield@gmail.com>