PCB contains FP registers, whose alignment must be 16 bytes at least.
Since the PCB pointed to by pc_pcb is immediately after the PCPU
itself, round-up the size of thge PCPU to a multiple of 16 bytes. The
PCPU is page aligned.
This fixes a misalignment trap caused by stopping a CPU in a SMP
kernel, such as been done when entering the debugger.
Reported by: Alan Robinson <alan.robinson@fujitsu-siemens.com>
4d9ed138d1