Merge pull request #1 from RT-Thread/master

sync
[GDB stub]first version
[bsp]add gdb support for stm32f4xx
[libcpu]am335x edit vector

vector_undef and vector_dabt
[bsp]add gdb support for BBB
Revert "[bsp]add gdb support for BBB"

This reverts commit a966dd3c3802198cf84adbd8aef08d9206e256ce.
[bsp]add gdb support for BBB
[bsp]stm32f4xx typo
Merge pull request #341 from armink/master

[YModem] YModem optimization;
[BSP] Add more error handling in STM32F1 bsp.
Update device.c
Merge pull request #2 from RT-Thread/master

sync
[bsp]Comment stm32f407 uart6
[gdb]Change open flag
[bsp]change BBB uart flag
import CM3-M7 project.
update uart driver.
add EMAC driver.
add delay for PHY check.
update EMAC driver.
update project.