不用NFS挂载，开发板可以启动，使用NFS出现
VFS: Mounted root (nfs filesystem) on device 0:13.
Freeing init memory: 160K
Failed to execute /linuxrc. Attempting defaults...
Kernel panic - not syncing: No init found. Try passing init= option to kernel.
See Linux Documentation/init.txt for guidance.
Backtrace:
[<c0016fe0>] (dump_backtrace+0x0/0x114) from [<c054a04c>] (dump_stack+0x18/0x1c)
r7:00000013 r6:c002ba1c r5:c074420c r4:c07b8ee0
[<c054a034>] (dump_stack+0x0/0x1c) from [<c054a0b0>] (panic+0x60/0x198)
[<c054a050>] (panic+0x0/0x198) from [<c00088c0>] (init_post+0xa8/0xcc)
r3:00000021 r2:0000001e r1:0000001d r0:c06a382d
[<c0008818>] (init_post+0x0/0xcc) from [<c0744314>] (kernel_init+0x108/0x13c)
r5:c074420c r4:c07b7620
[<c074420c>] (kernel_init+0x0/0x13c) from [<c002ba1c>] (do_exit+0x0/0x668)
eth0: no IPv6 routers present
