Add "bootloader" CLI command

[Adminiuga]

Add "bootloader" CLI command.
If NCP has bootloader available, it will launch it. For example on Nortek GoControl HUSBZB-1 sticks, after launching bootloader, it is available via terminal using 115200 baud connection rate.

debug: Using selector: EpollSelector
debug: Using selector: EpollSelector
debug: Connected. Resetting.
debug: Resetting EZSP
debug: Resetting ASH
debug: Sending: b'1ac038bc7e'
debug: RSTACK Version: 2 Reason: RESET_SOFTWARE frame: b'c1020b0a527e'
debug: Send command version: (4,)
debug: Sending: b'004221a850ed2c7e'
debug: Data frame: b'0142a1a8532825d4f4497e'
debug: Sending: b'8160597e'
debug: Application frame 0 (version) received: b'07023066'
debug: Send command version: (7,)
debug: Sending: b'7d31432157542a1205877e'
debug: Data frame: b'1243a157542a12b069f2a5a17e'
debug: Sending: b'82503a7e'
debug: Application frame 0 (version) received: b'07023066'
debug: Switched to EZSP protocol version 7
EZSP Stack Type: 2, Stack Version: 26160
debug: Send command getStandaloneBootloaderVersionPlatMicroPhy: ()
debug: Sending: b'2240215754bbef5f7e'
debug: Data frame: b'2340a15754bb05e65d9e49e6697e'
debug: Sending: b'83401b7e'
debug: Application frame 145 (getStandaloneBootloaderVersionPlatMicroPhy) received: b'1054040a03'
bootloader version: 0x5410, nodePlat: 0x04, nodeMicro: 0x0a, nodePhy: 0x03
debug: Send command launchStandaloneBootloader: (0,)
debug: Sending: b'3341215754a515fb937e'
debug: Data frame: b'3441a15754a515c0077e'
debug: Sending: b'8430fc7e'
debug: Application frame 143 (launchStandaloneBootloader) received: b'00'
bootloader launched successfully
debug: Closed serial connection

[Hedda]

@Adminiuga Should this not be optional and disabled by default for security/safety reasons so that a user (or a malicious program) does not accidentally mess up the bootloader and brick the device?

Silicon Labs looks to recommend that manufacturers write protect on the bootloader flash area when building firmware images for production but as you know that is not always followed. See:

• https://www.silabs.com/community/wireless/zigbee-and-thread/knowledge-base.entry.html/2017/12/28/building_firmwareim-1OPr