plat: stm32: update with libmaple

Merged commit:
commit aaeb08368429644a12d479573f3235096bbe01f0
Merge: 4ab37d2 5947249
Author: Marti Bolivar <mbolivar@leaflabs.com>

    Merge pull request #54 from ginge/master
plat: stm32: update with libmaple

Merged commit:
commit ffa57f5f4ac77ab25cafc5cd93dbd705753790a0
Author: Daniel Nyström <daniel@nystrom.st>

    libmaple/timer.c: Sync enable_irq() declaration with it's definition