fastboot: mt85xx: add command to flash/erase emmc hwpart

This patch includes the following:
1. Add fastboot command to erase the whole EMMC_USER
2. Add fastboot command to flash image at EMMC_BOOT1
3. Add fastboot command to erase the whole EMMC_BOOT1
4. Enale CONFIG_FASTBOOT_MMC_BOOT1_SUPPORT for mt8518

3 files changed