Compiler may do more optimization when the parameter is const.

[USB]fix rt_usbd_set_config() BUG which set the USB device to configurat...

update MSH ifconfig and add MSH netstat.

[shell] define FINSH_PROMPT as finsh_get_prompt when FINSH_USING_MSH enabled

When MSH enabled, the prompt will change at the two shells. So we should
use dynamic prompt when FINSH_USING_MSH defined.

Qemu realview vmm

When RT-Thread is running stand alone, it forgot to enable the
distributor of GIC.

This piece of code will enable the interrupt early before switching to
the first thread. Although it is harmless, but not prefect.

Qemu realview vmm

[USB]fix rt_usbd_set_config() BUG which set the USB device to configuration state before enumerating the device.

[vmm] add realview-pb-a8 VMM support

[msh] don't complain on empty command

Just branch out and no complain on command length == 0;

Msh next

When DFS_USING_WORKDIR is enabled, msh will try to chdir if the command
is not found. For example, if there is folder named "SD", and there is
no `SD` command and `SD.mo` module, typing "SD" in msh will cd to the
folder.

In more detail, the execution order right now is:

1. built-in command
2. module
3. cd to path

If you have a folder named "ps", you have to run `cd ps` to change the
working dir.

Msh can execute module directly. So try to auto-complete the path when
user press TAB. There is a chance that the path is a module.

modify the pixel format to RGB565 in sdl_fb.c