accel/tcg: Use interval tree for user-only page tracking

accel/tcg: Use interval tree for user-only page tracking

Finish weaning user-only away from PageDesc.

Using an interval tree to track page permissions means that
we can represent very large regions efficiently.

Resolves: https://gitlab.com/qemu-project/qemu/-/issues/290
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/967
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1214
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>