accel/tcg: Add clear_flags argument to page_set_flags

accel/tcg: Add clear_flags argument to page_set_flags

Expand the interface of page_set_flags to separate the
set of flags to be set and the set of flags to be cleared.

This allows us to replace PAGE_RESET with the PAGE_VALID
bit within clear_flags.

Replace PAGE_TARGET_STICKY with TARGET_PAGE_NOTSTICKY;
aarch64-linux-user is the only user.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>