Previously we need turn off the PMP locks in K230 vendor u-boot to use
NuttX, this complicates the setup process. This patch supports running
NuttX with original vendor u-boot so that to reduce setup complexity.
It also enables empty NSH prompt string in AMP master config as the apps
side support is ready.
Signed-off-by: Yanfeng Liu <yfliu2008@qq.com>