Fully autonomous STM32 bootloader sources
The bootloader does not rely anymore on the EwoK kernel BSP C code. This patch includes the following:
- all requested arch-specific files (including SoC and core specific implementations)
- a poll-based button pushed detection. This permits to delete EXTI support from the bootloader, reducing the amount of code and the security impact of handling external interrupts
The bootloader also supports fully automated CI integration using travis, through disco407 and wookey build check for both master commits and PR