Support mp lk start on RISC-V. Several changes throughout were required:
- Add signal in asm start to force secondary harts to wait for bss to be
cleared.
- Use mhartid in arch_curr_cpu_num, PLIC, and CLINT
- Use tp register as thread pointer instead of global variable.
- Support sending IPIs between harts using CLINT
- Add spinlock implementation
Most of changes were moving around where macros were defined, plus the
following:
- Remove requirement for floating point on RV64 to support booting
monitor core on U54 SoC.
- Add support for Debug LEDs on HiFive Unleashed Board
-added support for bringing up the clocks and setting up the gpio bits
before starting the uart.
-add a proper target init routine
-add scripts to flash board via openocd
-fixed bug in riscv interrupt save state where it wasn't saving mstatus
on irq entry.
-comment out cycle enabling, not implemented on this core
