add support for variable based device address (regs)

Signed-off-by: Julien Peeters <contact@julienpeeters.net>
move stm32 register helpers to separate file

Signed-off-by: Julien Peeters <contact@julienpeeters.net>
add bitfield for stm32 rcc registers

Signed-off-by: Julien Peeters <contact@julienpeeters.net>
update stm32 bitfield for the I2C controller

Signed-off-by: Julien Peeters <contact@julienpeeters.net>
fix typo and bugs in stm32 register helpers

Signed-off-by: Julien Peeters <contact@julienpeeters.net>
fix typo in stm32 register helpers

Signed-off-by: Julien Peeters <contact@julienpeeters.net>
add priliminary support for I2C bus on stm32

Signed-off-by: Julien Peeters <contact@julienpeeters.net>
add -Wfatal-errors in cflags

Signed-off-by: Julien Peeters <contact@julienpeeters.net>