- For RTL8188CUS/RTL8192CU, we have to force 8051 reset/enable before waiting

- For RTL8188CUS/RTL8192CU, we have to force 8051 reset/enable before waiting
  for firmware to get ready.  It fixes "urtwn0: could not load firmware page"
  while running stsp@'s script: dhclient urtwn0; ifconfig urtwn0 down;
  ifconfig urtwn0 scan in a loop.

- Minor cleanup for rtwn_read_rom()/rtwn_get_txpower(); no need to use
  callbacks.

Tested by stsp@ and me.

ok stsp@