[DISC_F407VG & ARCH_MAX] change default toolchain
[NUCLEO_F091RC] pin_mode for Serial only if the pin is present

Same as all other targets.
Merge pull request #538 from bcostm/master

HAL: NUCLEO_F091RC - pin_mode for Serial only if the pin is present
[HAL][ARCH_MAX] use different PeripheralNames.h for STDIO_UART
Merge pull request #537 from xiongyihui/stm32f407

HAL: DISC_F407VG, ARCH_MAX - change default toolchain

- ARCH_MAX - use different PeriheralNames.h files
Merge remote-tracking branch 'upstream/master'