Using NFS in conjunction with boot spec and the feature to let Barebox
auto generate a kernel command line must keep the options the NFS filesystem
was mounted in Barebox. This patch extends the kernel command line parameter
on demand if something different than the defaults are used.

The command:

barebox:/ boot nfs://myhost//root

expands to the kernel command line:

nfsroot=myhost:/root,v3,tcp

while the command:

barebox:/ boot nfs://myhost:2049//root

expands now to the kernel command line:

nfsroot=myhost:/root,v3,tcp,mountport=2049,port=2049

Signed-off-by: Juergen Borleis <jbe@pengutronix.de>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>