Duo 256m not support ION=0

[Arielfoever]

https://github.com/milkv-duo/duo-buildroot-sdk/blob/develop/build/boards/cv181x/cv1812cp_milkv_duo256m_sd/memmap.py#L43 修改为 0 * SIZE_1M 会导致 https://github.com/milkv-duo/duo-buildroot-sdk/blob/develop/build/boards/cv181x/cv1812cp_milkv_duo256m_sd/memmap.py#L57 的断言失败，最小值应该是22。望周知。

修改相关文档， 排查故障解决ION无法彻底关闭的问题。

[carbonfix]

diff --git a/build/boards/cv181x/cv1812cp_milkv_duo256m_sd/memmap.py b/build/boards/cv181x/cv1812cp_milkv_duo256m_sd/memmap.py
index fcc097d01..545af061c 100755
--- a/build/boards/cv181x/cv1812cp_milkv_duo256m_sd/memmap.py
+++ b/build/boards/cv181x/cv1812cp_milkv_duo256m_sd/memmap.py
@@ -40,10 +40,10 @@ class MemoryMap:
     # =================
     # Multimedia buffer. Used by u-boot/kernel/FreeRTOS
     # =================
-    ION_SIZE = 75 * SIZE_1M
-    H26X_BITSTREAM_SIZE = 2 * SIZE_1M
+    ION_SIZE = 0 * SIZE_1M
+    H26X_BITSTREAM_SIZE = 0 * SIZE_1M
     H26X_ENC_BUFF_SIZE = 0
-    ISP_MEM_BASE_SIZE = 20 * SIZE_1M
+    ISP_MEM_BASE_SIZE = 0 * SIZE_1M
     FREERTOS_RESERVED_ION_SIZE = H26X_BITSTREAM_SIZE + H26X_ENC_BUFF_SIZE + ISP_MEM_BASE_SIZE

     # ION after FreeRTOS
diff --git a/ramdisk/rootfs/overlay/cv181x_musl_riscv64/system/ko/loadsystemko.sh b/ramdisk/rootfs/overlay/cv181x_musl_riscv64/system/ko/loadsystemko.sh
index b07a47db8..a539510d1 100644
--- a/ramdisk/rootfs/overlay/cv181x_musl_riscv64/system/ko/loadsystemko.sh
+++ b/ramdisk/rootfs/overlay/cv181x_musl_riscv64/system/ko/loadsystemko.sh
@@ -24,7 +24,7 @@ insmod /mnt/system/ko/cv181x_vcodec.ko
 insmod /mnt/system/ko/cv181x_jpeg.ko
 insmod /mnt/system/ko/cvi_vc_driver.ko MaxVencChnNum=9 MaxVdecChnNum=9
 #insmod /mnt/system/ko/cv181x_rtc.ko
-insmod /mnt/system/ko/cv181x_ive.ko
+#insmod /mnt/system/ko/cv181x_ive.ko

 echo 3 > /proc/sys/vm/drop_caches
 dmesg -n 4