provide /n and /mnt early in bootrc to allow consistent use in /lib/namespace

provide /n and /mnt early in bootrc to allow consistent use in /lib/namespace

theres a bootstrap problem:

when /bin/init is run, it processes /lib/namespace where we might want to
mount or bind resources to /n or /mnt. but mntgen was run later in
cpurc/termrc so these mounts would be ignored.

we already have mntgen in bootfs, so we can provide these mountpoints early.

i keep the termrc/cpurc mntgens where they are, but ignore the error
prints. this way old kernels will continue to work.