mambo: Allow loading multiple CPIOs
mambo: Allow loading multiple CPIOs

Currently we have support for loading a single CPIO and telling Linux to
use it as the initrd. But the Linux code actually supports having
multiple CPIOs contiguously in memory, between initrd-start and end, and
will unpack them all in order. That is a really nice feature as it means
you can have a base CPIO with your root filesystem, and then tack on
others as you need for various tests etc.

So expand the logic to handle SKIBOOT_INITRD, and treat it as a comma
separated list of CPIOs to load. I chose comma as it's fairly rare in
filenames, but we could make it space, colon, whatever. Or we could add
a new environment variable entirely. The code also supports trimming
whitespace from the values, so you can have "cpio1, cpio2".

Signed-off-by: Michael Ellerman <864f124608374e06e4da1fa5d2e47ed839b95411@ellerman.id.au>
Signed-off-by: Stewart Smith <ec31ab75ddf977353c8f660f92ea8b23f64aef25@linux.vnet.ibm.com>

shenki/skiboot,qemu/skiboot,shenki/skiboot,qemu/skiboot,mikey/skiboot,shenki/skiboot,open-power/skiboot,legoater/skiboot,stewart-ibm/skiboot,qemu/skiboot,open-power/skiboot,open-power/skiboot,qemu/skiboot,mikey/skiboot,legoater/skiboot,shenki/skiboot,open-power/skiboot,legoater/skiboot,stewart-ibm/skiboot,mikey/skiboot,qemu/skiboot,legoater/skiboot,stewart-ibm/skiboot,legoater/skiboot,open-power/skiboot,shenki/skiboot