[stm32] fix i2c_reset

rcc_periph_reset_pulse needs RST_I2Cx instead of RCC_I2Cx as argument
see also #329
[stm32] fix dox for rcc_periph_x

closes #329
add MSC (Mass Storage Class) support
Allow more than one usbd_register_set_config_callback

In a composite device if one want to separate code
for each interface, usbd_register_set_config_callback
can now register more than one callback.

Signed-off-by: Franck Jullien <franck.jullien@gmail.com>
USB: Fix definition of function according to previous commit.
[l1-flash/eeprom] Add lock/unlock/eeprom helper routines
stm32: timers: Fix edge polarity setup

The CCxP/CCxNP bits are actually separated by a reserved bit, so the
correct mask is 0xa, (0b1010) not 0x6 (0b0110)

Reported by PyroDevil on the mailinglist
Merge remote-tracking branch 'upstream/master'