RT1020 Flash loader improvement method

In some use case, when user program size>128K，it will display verify error when download, and the user code can’t run normally. Especially the second time download in IAR, after user modify the FlexRAM allocation. The root cause is IAR default Flash Loader use all the default 128K OCRAM as the download buffer in .ICF, if user changed the FlexRAM allocation in user code, for example: setting OCRAM to 32K, it will lead to error as there is no 128K buffer size, this demo code is used to fix it.

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