LPC546XX sector writes issues which causes bootloader update failure

A sequence of flash_erase_sector and flash_program_page in [critical_erase_and_program](https://github.com/ARMmbed/DAPLink/blob/master/source/daplink/drag-n-drop/iap_flash_intf.c#L473) will produce a mismatch in the binary being written (can be checked by LPCScrypt_CLI.cmd ).

Another issue is [programming a memory from rom location](https://github.com/ARMmbed/DAPLink/blob/master/source/daplink/drag-n-drop/iap_flash_intf.c#L460) will cause a fault, and will revert the interface chip to an LPC USB device, to be flashed by LPCScrypt.