console: native_posix: change init priority to 99

This changes the init priority of native posix console to 99.
When building for native_posix, it is usually assumed that
the output would be stdout. With old priority at 60, UART
console, for example, can be initialized later which means
printk() would not go to stdout. So changing the native posix
console to be (hopefully) initialized last.

Signed-off-by: Daniel Leung <daniel.leung@intel.com>