[PATCH] neofb: avoid resetting display config on unblank (v2)

There were two mistakes in the register-read-on-(un)blank approach.

- First, without proper register (un)locking the value read back will always
  be zero, and this is what I missed entirely until just now.  Due to this,
  the logic could not be verified at all and I tried some bogus checks which
  are completely stupid.

- Second, the LCD status bit will always be set to zero when the backlight
  has been turned off.  Reading the value back during unblank will disable the
  LCD unconditionally, regardless of the state it is supposed to be in, since
  we set it to zero beforehand.

So this is what we do now:

- create a new variable in struct neofb_par, and use that to determine
  whether to read back registers (initialized to true)

- before actually blanking the screen, read back the register to sense any
  possible change made through Fn key combo

- use proper neoUnlock() / neoLock() to actually read something

- every call to neofb_blank(...