Using pflash with u-boot,when CONFIG_SYS_FLASH_USE_BUFFER_WRITE were defined,envirment args won't be able to save correctly

Generated a u-boot image with qemu_arm_defconfig,did some modification to qemu-arm.h.
Before added "CONFIG_SYS_FLASH_USE_BUFFER_WRITE",call saveenv in u-boot command line can save the envirment but painful slow.

after added it,seems the action took no time,but the data won't be saved correctly,reset the board to boot again(i'd waited a while to reset the board) ,the u-boot will tell you enviremnt checksum mismatch,using the default.