Cleaner L2_MASK definition in header file
Fix _do_real_tlb_miss_handler

- the case where the tlb miss comes from kernel context AND vaddr
  is in the 0xc000.0000-0xc800.0000 is now handled in the assembly
  code in locore.s in _real_tlb_miss_handler.

- "psw" variable was not written back to PSW CSR register.

- L2_MASK was not applied while indexing L2 page table
  to get the PTE.
Using mvhi rN, hi(imm16) is wrong. It results in rN = 0
Fix buggy assembly instruction. I want r2 += 56
Fix _real_tlb_miss_handler

- r3 value was meant to be written to PSW before "calling"
  _do_real_tlb_miss_handler.

- RA should contain physical address, because we will return from
  _do_real_tlb_miss_handler with TLB off.
Fix _real_tlb_miss_handler again
During the boot, current pmap is the kernel's one

This initializes the "current pmap" of the "current cpu" to be the kernel's pmap