[DeviceDrivers] Add more SPI drivers. 

Move PNG_NO_WRITE_SUPPORTED outside of RT_USING_NEWLIB. #197

[BSP] tm4c129x Add EMAC/PHY driver

1. Resize RT_LWIP_SEG_NUM drom 8 to 12
2. modify gcc compile switch, using C99

1. Add ETH MAC driver using DMA for Tx and Rx lwip pBuf.
2. Modify the tivaware emac library to fix the bug that PHY read is not stable when sysclk is 120MHz
3. In PHY IRQ handler, insert a dummy reading (REG_BMSR) before read PHY_STS to force update STS register.

This reverts commit 666d1298.

1. Add ETH MAC driver using DMA for Tx and Rx lwip pBuf.
2. Modify the tivaware emac library to fix the bug that PHY read is not stable when sysclk is 120MHz
3. In PHY IRQ handler, insert a dummy reading (REG_BMSR) before read PHY_STS to force update STS register.

[bsp] Add BSP for TM4C1294XL (TI Tiva C Series Connected LaunchPad)

[Kernel] The rt_object_find routine can support to find an object inside a module. The usage is: rt_object_find("module_name/object_name").

pull rt-thread master

[bsp] modify the uart_driver to fit the new rt-thread serial device driver framework. Modify the template.uvproj for auto generate MDK project.

[Drivers] re-write serial framework.

[Kernel] src/timer: fix a compile warning

Next ymodem

[bsp] add the linker script file.