Fix: blackpillv2 pinout

[lenvm]

Detailed description

This pull request changes the pinout of the blackpillv2 platform.

The changes are done as described in the comments of #1418.

Table 1: comparing current pinout to proposed pinout

function	current (e490465)	proposal
nRst	PB4	PA5
nTRST	PB5 (optional)	PA6 (optional)
TDI	PA1 (also used by LED UART)	PB6
TDO	PB3	PB7
TCK	PA14	PB8
TMS	PA13	PB9
PWR	PB8	PA1
UART TX	PB6	PA2
UART RX	PB7	PA3
LED UART	PA1 (also used by TDI)	PA4
LED idle run	PC13	PC13
LED error	PC14	PC14
LED boot loader	PC15	PC15
USER KEY	PA0	PA0
USB VBUS	PA9	PA9
USB ID	PA10	PA10
USB D-	PA11	PA11
USB D+	PA12	PA12
JTAG TMS	-	PA13
JTAG TCK	-	PA14
JTAG TDI	PA15	PA15
JTAG TDO	-	PB3
JTAG TRST	-	PB4

Figure 1: proposed pinout

Benefits:

• This pull request fixes the issue described in blackpillv2: PA1 is defined for both TDI and LED_UART #1418. Therefore the is no pin conflict anymore between LED UART and TDI.
• JTAG pins (PA13, PA14, PA15, PB3, PB4) are not used, such that these pins stay available to program and debug the board.
• Pins of the STM32F411Cx that are 5V-intolerant (PB5) are not used, to reduce susceptibility to damage.
• Pins of similar type are located closer to each other on the board.

Your checklist for this pull request

• I've read the Code of Conduct
• I've read the guidelines for contributing to this repository
• It builds for hardware native (make PROBE_HOST=native)
• It builds for hardware blackpillv2 (make PROBE_HOST=blackpillv2)
• It builds as BMDA (make PROBE_HOST=hosted)
• I've tested it to the best of my ability: the code compiles, can be flashed and runs on a board with STM32F401CC microcontroller.
• My commit messages provide a useful short description of what the commits do

Closing issues

• fixes blackpillv2: PA1 is defined for both TDI and LED_UART #1418

[dragonmux]

LGTM. As nobody's complained about the re-jigging of the pinout and as this fixes bugs caused by the pinout, we're going to optimistically merge this and let people open issue tickets if they have any issues.