firmware: qcom: tzmem: don't ask about allocator mode when not enabled

The Qualcomm firmware code shouldn't ask about what memory allocator
mode should be used when the code isn't even enabled.

Get rid of pointless config-time question.

Link: https://lore.kernel.org/all/CAHk-=wg+38EHPKGou1MqXwAAXC30cM8sMgZAGnZ7TcFO4L9J2w@mail.gmail.com/


Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>