This commit fixes configuration problems when trying to use i2c pins that need to be remapped.
All B8 and B9 pins for STM32F1 need to be remapped, so a check is done if the remappable pins are selected.
In commit e90f2b439e the I2C config has been
adapted to the new I2C API. However, the pins of I2C_DEV(0) have been changed
from PB6 and PB7 to PB8 and PB9. While PB8 and PB9 also can be used for I2C1
by remapping I2C1, this is not done. As a result, I2C1 was unusable. This
commit restores the default I2C1 pins for I2C_DEV(0), resulting in I2C_DEV(0)
becoming usable again.
