Board Support Package

* Two Steps
- Basic init
1) Disable interrupts and cache
2) Init memory controller and cache
3) Init stack register and other registers
4) Init URAT for debugging
This step generally uses Assembly to implement the above tasks
- Board init
1) Clear memory
2) Init interrupts
3) Init timers
4) Init other hardwares
5) Init RTOS
This step would run C codes