Xiaomi Corp. is preparing a self-designed mobile processor for its upcoming smartphones in an effort to reduce its reliance on foreign suppliers Qualcomm Inc. and MediaTek Inc.The processor may help Xiaomi be more self-sufficient and stand out in an Android market led by Qualcomm customers. Mass production of the chip designed in-house is expected to begin in 2025, according to people familiar with the matter, who asked not to be named discussing a private corporate plan....