Boards with an integrated debugger/programmer that also provides the
serial as UART <--> USB adapter, the TTY serial matches the serial of
the programmer.
This adapts the `serial.inc.mk` to set the `DEBUG_ADAPTER_ID` to the
TTY serial if (and only if) `MOST_RECENT_PORT` *and*
`DEBUG_ADAPTER_ID_IS_TTY_SERIAL` both have a value of `1`. Boards with
an integrated programmer are expected to set
`DEBUG_ADAPTER_ID_IS_TTY_SERIAL` to `1` in their `Makefile.include`.
This allows automatically selecting TTY actually belonging to an
Arduino Mega2560 if `MOST_RECENT_PORT=1` is set.
Note: Unless `ARDUINO_MEGA2560_COMPAT_WITH_CLONES` is set to `0`,
this will fall back to detecting any cheap USB UART bridge typically
found in Arduino Mega 2560 clones if no genuine Arduino Mega is found.
cpu/$(CPU)/Makefile.features and cpu/$(CPU)/Makefile.dep are
automatically included
Part of moving CPU/CPU_MODEL definition to Makefile.features to have it
available before Makefile.include.
The CPU variable in the boards Makefile.include file already contains the target
CPU, so there is no reason to provide it in each board again as avrdude flag.
This commit automatically sets the avrdude target from the CPU variable and
removes the unneeded flags.
Leverages common flasher (avrdude) and removes unnecessary exports.
Moreover, a reuse of serial.inc.mk is perfomed from the same
atmega_common/Makefile.include
