This is an OFW initrd module that would load the initrd from device tree
parameters and give the to the md driver.
With this patch, it is possible to pass a rootfs image through kexec in PowerNV
mode (powerpc64). In order to user it, you should set the MD_ROOT_MEM option in
your kernel configuration.
Reviewed by: jhibbits
Approved by: jhibbits (mentor)
Differential Revision: https://reviews.freebsd.org/D15705
