Bootloader v4.1.3

Changes:

• Update Mbed OS to 5.15.2
• Allow boot messages on SWO instead of serial port.
• Disable standard output to save code size.
• Don't check boot counter on software reset.
• Allow configuring alternate entry point for bootloader instead of main.
• Add support for DISCO_F769NI.
• Add configuration for MIMXRT1050_EVK.
• Add configuration for L496AG.
• Add configuration for Uhuru Raven.
• Add configuration for Renesas GR-PEACH and LYCHEE.
• Add configuration for EP_AGORA target.
• Drop block_device_fake_rot.json configuration file.
• Allow specifying a startup delay before initializing storage hardware.
• NRF52840_DK: Adds information about UICR registers
• NRF52840_DK: Adds as release target and adds a new app config
• Small code cleanup and refactoring