lib, initramfs: Add initramfs LZO compression

this small patchset adds support for compressing initial ramdisks
into LZO (Lempel Ziv Oberhumer) format. It has been tested on x86
and x86_64. The patches apply to current git mainline.

In a pair of real-world examples, an Eee 901 boots ~120 ms faster.
A high-end desktop only saves an inconsequential 35 ms.

Specs: 

* LZO data decompresses in 55 - 60% of the time needed by gzip,
  when using the 'fast' decompressor.
* The decompressor is very small, < 2 kB on x86.
* An LZO-compressed initramfs takes 7-10% more disk space vs gzip.

Test results:

initramfs.cpio: 14174 kB 
initramfs.gz:    4657 kB
initramfs.lzo:   5007 kB

            Eee 901    Core i7 920
           SSD 30MB/s  HDD 60MB/s

            gz  lzo     gz  lzo

disk read  152  163     76   82
unpacking  247  113     95   54
----------------------------------
total      399  276    171  136

net gain     123          35 

All values are milliseconds. Disk read times are estimates.

I have a patch that adds support for LZO-compressed kernels but
decided to not include it now since it's only implemented for x86.

Cheers,
Andreas

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