Expand :bootloader target to use keyboard's hardware config

[drashna]

Right now, the :bootloader target assumes the ATMega32U4, 5v controller. That's fine if you want to use that controller.

However, it would be nice if it imported the MCU, F_CPU, and other settings from the board in question. This includes the firmware size, and bootloader offset info.

The settings are here:
https://github.com/qmk/qmk_firmware/blob/master/lib/lufa/Bootloaders/DFU/makefile#L18

Feature Request Type

• Alteration (enhancement/optimization) of existing feature(s)

[drashna]

Okay, looking into this a bit, this won't be simple. We can't just pass the data along, in memory.

Specifically, we'll have to add something like the keyboard.h genearation, but for a rules.mk or build.mk that includes all of the info that we need.

Namely:

MCU          ?= atmega32u4
ARCH         ?= AVR8
BOARD        ?= QMK
F_CPU        ?= 16000000
F_USB        ?= $(F_CPU)

FLASH_SIZE_KB         ?= 32
BOOT_SECTION_SIZE_KB  ?= 4

@jackhumbert is there an easy way to pull this information?

I know that grabbing the bootloader size should be easy enough. That's set by bootlooder.mk, actually.
But the firmware size is ... complicated.

It's:

	$(eval MAX_SIZE=$(shell n=`$(CC) -E -mmcu=$(MCU) $(CFLAGS) $(OPT_DEFS) tmk_core/common/avr/bootloader_size.c 2> /dev/null | sed -ne '/^#/n;/^AVR_SIZE:/,$${s/^AVR_SIZE: //;p;}'` && echo $$(($$n)) || echo 0))

Which is AVR only (and part of why ChibiOS can't check).