powerpc: better handling of shutdown flags

[mhorne]

Summary

RB_HALT does not mean poweroff, RB_POWEROFF does.

[jhibbits]

sys/powerpc/powermac/cuda.c

751–757

This one doesn't match the others. The others handle poweroff, reset, and halt. You want something more like (there's a better way, of course):

if ((howto & RB_POWEROFF) != 0)
  cmd[1] = CMD_POWEROFF;
else if ((howto & RB_HALT) == 0)
  cmd[1] = CMD_RESET;

if (cmd[1] != 0) {
   cuda_poll....
   cuda_send....
}

while (1)
   cuda_poll...

[mhorne]

For cuda, format the checks the same way.