uboot/prism: add a root= cmdline param

Add a root=rootfsX bootarg where X is equal to the activated kernel
number. GFLT110/300 do not have a separate rootfs, if we don't specify
one explicitly, then ginstall gets to decide what partition to format.

Change-Id: I163cefa23faeec4485637e01c8b65eaf9a711076
1 file changed